TheInfoList

In
communication Communication (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to b ...

s and
information processing Information processing is the change (processing) of information Information is processed, organised and structured data. It provides context for data and enables decision making process. For example, a single customer’s sale at a resta ...
, code is a system of rules to convert
information Information is processed, organised and structured data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sense, data are a set of values of qualitative property, qualitative or quant ...

—such as a
letter Letter, letters, or literature may refer to: Characters typeface * Letter (alphabet) A letter is a segmental symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, Object (philosophy ...
,
word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), meaning. In many languages, words also co ...

, sound, image, or
gesture A gesture is a form of non-verbal communication Nonverbal communication (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact, facial expressions, gestures, Posture (psychology), posture, and body ...
—into another form, sometimes shortened or
secret Secrecy is the practice of hiding information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of its characteristics. The con ...
, for communication through a
communication channel Different types of physical transmission media supporting communication channels A communication channel refers either to a physical transmission medium A transmission medium is a system or substance that can mediate the propagation of signa ...
or storage in a
storage medium On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data storage medium. Data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more te ...
. An early example is an invention of
language A language is a structured system of communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...

, which enabled a person, through
speech Speech is human vocal communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, ...

, to communicate what they thought, saw, heard, or felt to others. But speech limits the range of communication to the distance a voice can carry and limits the audience to those present when the speech is uttered. The invention of
writing Writing is a medium of human communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area arou ...

, which converted spoken language into
visual The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined ba ...
symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. All (and ) is achieved th ...

s, extended the range of communication across space and
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...

. The process of encoding converts information from a
source Source or subsource or ''variation'', may refer to: Research * Historical document * Historical source * Source (intelligence) or subsource, typically a confidential provider of non open-source intelligence * Source (journalism), a person, public ...
into symbols for communication or storage. Decoding is the reverse process, converting code symbols back into a form that the recipient understands, such as English or/and Spanish. One reason for coding is to enable communication in places where ordinary
plain language Plain language is writing designed to ensure the reader understands as quickly, easily, and completely as possible. Plain language strives to be easy to read, understand, and use. It avoids Verbosity, verbose, convoluted language and jargon. In man ...
, spoken or written, is difficult or impossible. For example,
semaphore Semaphore is the use of an apparatus with telegraphy Telegraphy is the long-distance transmission of textual messages where the sender uses a semaphore system, known to the recipient, rather than a physical exchange of an object bearing ...
, where the configuration of
flags A flag is a piece of fabric A textile is a flexible material made by creating an interlocking network of yarn Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting ...
held by a signaler or the arms of a
semaphore tower An optical telegraph is a semaphore system using a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals. There are two main types of such systems; the semaphore telegraph which uses piv ...
encodes parts of the message, typically individual letters, and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent.

# Theory

In
information theory Information theory is the scientific study of the quantification (science), quantification, computer data storage, storage, and telecommunication, communication of Digital data, digital information. The field was fundamentally established by the ...
and
computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of computation, automation, a ...
, a code is usually considered as an
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

that uniquely represents
symbols A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), meanin ...

from some source
alphabet An alphabet is a standardized set of basic written symbols A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semanti ...
, by ''encoded'' strings, which may be in some other target alphabet. An extension of the code for representing sequences of symbols over the source alphabet is obtained by concatenating the encoded strings. Before giving a mathematically precise definition, this is a brief example. The mapping :$C = \$ is a code, whose source alphabet is the set $\$ and whose target alphabet is the set $\$. Using the extension of the code, the encoded string 0011001 can be grouped into codewords as 0 011 0 01, and these in turn can be decoded to the sequence of source symbols ''acab''. Using terms from
formal language theory In logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, la ...
, the precise mathematical definition of this concept is as follows: let S and T be two finite sets, called the source and target
alphabets An alphabet is a standardized set of basic written symbols A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic ...
, respectively. A code $C:\, S \to T^*$ is a
total function In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related structures (), shapes and spaces in which they are contained (), and quantities and their changes ( and ). There is no g ...

mapping each symbol from S to a sequence of symbols over T. The extension $C\text{'}$ of $C$, is a
homomorphism In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. I ...
of $S^*$ into $T^*$, which naturally maps each sequence of source symbols to a sequence of target symbols.

## Variable-length codes

In this section, we consider codes that encode each source (clear text) character by a
code word In communication, a code word is an element of a standardized code or Communications protocol, protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning. Code words are typically used fo ...
from some dictionary, and
concatenation In formal language theory and computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves ...
of such code words give us an encoded string. Variable-length codes are especially useful when clear text characters have different probabilities; see also
entropy encoding In information theory, an entropy coding (or entropy encoding) is a lossless compression , lossless data compression scheme that is independent of the specific characteristics of the medium. One of the main types of entropy coding creates and assi ...
. A ''prefix code'' is a code with the "prefix property": there is no valid code word in the system that is a
prefix A prefix is an affix In linguistics Linguistics is the scientific study of language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign language) ...
(start) of any other valid code word in the set.
Huffman coding In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
is the most known algorithm for deriving prefix codes. Prefix codes are widely referred to as "Huffman codes" even when the code was not produced by a Huffman algorithm. Other examples of prefix codes are
country calling codes Country calling codes or country dial-in codes are telephone number A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device ...
, the country and publisher parts of s, and the Secondary Synchronization Codes used in the
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

WCDMA The Universal Mobile Telecommunications System (UMTS) is a mobile cellular system for networks based on the standard. Developed and maintained by the (3rd Generation Partnership Project), UMTS is a component of the standard set and compares w ...
3G Wireless Standard. Kraft's inequality characterizes the sets of codeword lengths that are possible in a prefix code. Virtually any uniquely decodable one-to-many code, not necessarily a prefix one, must satisfy Kraft's inequality.

## Error-correcting codes

Codes may also be used to represent data in a way more resistant to errors in transmission or storage. This so-called
error-correcting code In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwa ...
works by including carefully crafted redundancy with the stored (or transmitted) data. Examples include
Hamming code In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
s, Reed–Solomon, Reed–Muller, Walsh–Hadamard, Bose–Chaudhuri–Hochquenghem,
Turbo A turbocharger (technically a turbosupercharger), colloquially known as turbo, is a turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin Latin (, or , ) is a classical language A classical language is a language ...
, Golay, Goppa,
low-density parity-check code In information theory Information theory is the scientific study of the quantification, storage, and communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an apparent answer to the ...
s, and space–time codes. Error detecting codes can be optimised to detect ''burst errors'', or ''random errors''.

# Examples

## Codes in communication used for brevity

A cable code replaces words (e.g. ''ship'' or ''invoice'') with shorter words, allowing the same information to be sent with fewer
characters Character(s) may refer to: Arts, entertainment, and media Literature * Character (novel), ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk * Characters (Theophrastus), ''Characters'' (Theophrastus), a classical Greek set of char ...
, more quickly, and less expensively. Codes can be used for brevity. When
telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore Flag semaphore (from the Ancient ...
messages were the state of the art in rapid long-distance communication, elaborate systems of commercial codes that encoded complete phrases into single mouths (commonly five-minute groups) were developed, so that telegraphers became conversant with such "words" as ''BYOXO'' ("Are you trying to weasel out of our deal?"), ''LIOUY'' ("Why do you not answer my question?"), ''BMULD'' ("You're a skunk!"), or ''AYYLU'' ("Not clearly coded, repeat more clearly.").
Code word In communication, a code word is an element of a standardized code or Communications protocol, protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning. Code words are typically used fo ...
s were chosen for various reasons:
length Length is a measure of distance Distance is a numerical measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event, which can be us ...

, pronounceability, etc. Meanings were chosen to fit perceived needs: commercial negotiations, military terms for military codes, diplomatic terms for diplomatic codes, any and all of the preceding for espionage codes. Codebooks and codebook publishers proliferated, including one run as a front for the American
Black Chamber The Black Chamber (1919–1929), also known as the Cipher Bureau, was the United States' first peacetime cryptanalytic organization, and a forerunner of the National Security Agency The National Security Agency (NSA) is a national-level intell ...

run by
Herbert Yardley Herbert Osborn Yardley (April 13, 1889 – August 7, 1958) was an American cryptologist. He founded and led the cryptographic organization the Black Chamber. Under Yardley, the cryptanalysts of The American Black Chamber broke Japanese diplomati ...
between the First and Second World Wars. The purpose of most of these codes was to save on cable costs. The use of data coding for
data compression In signal processing Signal processing is an electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electro ...
predates the computer era; an early example is the telegraph
Morse code Morse code is a method used in telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: ...
where more-frequently used characters have shorter representations. Techniques such as
Huffman coding In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
are now used by computer-based
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

s to compress large data files into a more compact form for storage or transmission.

## Character encodings

Character encodings are representations of textual data. A given character encoding may be associated with a specific character set (the collection of characters which it can represent), though some character sets have multiple character encodings and vice versa. Character encodings may be broadly grouped according to the number of bytes required to represent a single character: there are single-byte encodings, multibyte (also called wide) encodings, and variable-width (also called variable-length) encodings. The earliest character encodings were single-byte, the best-known example of which is
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding Character encoding is the process of assigning numbers to graphical Graphics (from Greek Greek may refer to: Greece Anything of, ...
. ASCII remains in use today, for example in
HTTP headers HTTP header fields are components of the header section of request and response messages in the Hypertext Transfer Protocol The Hypertext Transfer Protocol (HTTP) is an application layer protocol for distributed, collaborative, hypermedia ...
. However, single-byte encodings cannot model character sets with more than 256 characters. Scripts that require large character sets such as Chinese, Japanese and Korean must be represented with multibyte encodings. Early multibyte encodings were fixed-length, meaning that although each character was represented by more than one byte, all characters used the same number of bytes ("word length"), making them suitable for decoding with a lookup table. The final group, variable-width encodings, is a subset of multibyte encodings. These use more complex encoding and decoding logic to efficiently represent large character sets while keeping the representations of more commonly used characters shorter or maintaining backward compatibility properties. This group includes
UTF-8 UTF-8 is a variable-width character encoding Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be ...
, an encoding of the
Unicode Unicode, formally the Unicode Standard, is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expressed in most of the world's wri ...

character set; UTF-8 is the most common encoding of text media on the Internet.

## Genetic code

Biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...

organisms contain genetic material that is used to control their function and development. This is
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

, which contains units named
gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

s from which
messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA i ...
is derived. This in turn produces
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

s through a
genetic code The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or rel ...

in which a series of triplets (
codon The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or reli ...

s) of four possible
nucleotides Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

can be translated into one of twenty possible
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

s. A sequence of codons results in a corresponding sequence of amino acids that form a protein molecule; a type of codon called a
stop codon Stop may refer to: Places *Stop, Kentucky Stop is an unincorporated area, unincorporated community located in Wayne County, Kentucky, United States. The origin of the name "Stop" is obscure. References Unincorporated communities in Wa ...
signals the end of the sequence.

## Gödel code

In
mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and their changes (cal ...
, a Gödel code was the basis for the proof of Gödel's
incompleteness theorem Complete may refer to: Logic * Completeness (logic) * Complete theory, Completeness of a theory, the property of a theory that every formula in the theory's language or its negation is provable Mathematics * The completeness of the real numbers, ...
. Here, the idea was to map
mathematical notation Mathematical notation is a system of symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or prag ...
to a
natural number In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the ''third'' largest city in the country"). In common mathematical terminology, w ...
(using a
Gödel numbering In mathematical logic Mathematical logic is the study of formal logic within mathematics. Major subareas include model theory, proof theory, set theory, and recursion theory. Research in mathematical logic commonly addresses the mathematical ...
).

## Other

There are codes using colors, like
traffic lights Traffic lights, traffic signals, stoplights or robots are signalling devices positioned at road intersections, pedestrian crossings, and other locations to control flows of traffic. The world's first traffic light was a manually operated ...

, the
color code A color code or colour code is a system for displaying information by using different color Color ( American English), or colour ( Commonwealth English), is the characteristic of visual perception described through color ''categories'', w ...
employed to mark the nominal value of the
electrical resistor A resistor is a passivity (engineering), passive terminal (electronics), two-terminal electronic component, electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce cu ...

s or that of the trashcans devoted to specific types of garbage (paper, glass, organic, etc.). In
marketing Marketing is the process of intentionally stimulating demand for and purchases of goods and services; potentially including selection of a target audience; selection of certain attributes or themes to emphasize in advertising; operation of adv ...

,
coupon In marketing, a coupon is a ticket or document that can be redeemed for a financial discounts and allowances, discount or rebate (marketing), rebate when purchasing a product (business), product. Customarily, coupons are issued by manufacturers ...

codes can be used for a financial discount or rebate when purchasing a product from a (usual internet) retailer. In military environments, specific uses: to mark some moments of the day, to command the infantry on the battlefield, etc. Communication systems for sensory impairments, such as
sign language Sign languages (also known as signed languages) are languages that use the visual-manual modality to convey meaning. Sign languages are expressed through manual articulations in combination with non-manual elements. Sign languages are full-fled ...

for deaf people and
braille Braille ( ; Braille: ⠃⠗⠇; ) is a tactile writing system A writing system is a method of visually representing verbal communication Communication (from Latin Latin (, or , ) is a classical language A classical langua ...

for blind people, are based on movement or tactile codes. are the most common way to encode
music Music is the of arranging s in time through the of melody, harmony, rhythm, and timbre. It is one of the aspects of all human societies. General include common elements such as (which governs and ), (and its associated concepts , , and ...

. Specific games have their own code systems to record the matches, e.g.
chess notation Chess notations are various systems that have developed to notation, record either the moves made in a game of chess or the position of chess piece, pieces on a chessboard. The earliest systems of notation used lengthy narratives to describe each m ...
.

## Cryptography

In the
history of cryptography Cryptography, the use of codes and ciphers to protect secrets, began thousands of years ago. Until recent decades, it has been the story of what might be called — that is, of methods of that use pen and paper, or perhaps simple mechanical aid ...
,
codes In communications and information processing, code is a system of rules to convert information—such as a letter (alphabet), letter, word, sound, image, or gesture—into another form, sometimes data compression, shortened or secrecy, secret, f ...
were once common for ensuring the confidentiality of communications, although
cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

s are now used instead. Secret codes intended to obscure the real messages, ranging from serious (mainly
espionage Espionage or spying is the act of obtaining secret Secrecy is the practice of hiding information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both it ...

in military, diplomacy, business, etc.) to trivial (romance, games) can be any kind of imaginative encoding:
flowers A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plants with a similar appearance that flower prof ...
, game cards, clothes, fans, hats, melodies, birds, etc., in which the sole requirement is the pre-agreement on the meaning by both the sender and the receiver.

# Other examples

Other examples of encoding include: *Encoding (in
cognition Cognition () refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses many aspects of intellectual function Intellectual functioning refers to the "general men ...
) - a basic perceptual process of interpreting incoming stimuli; technically speaking, it is a complex, multi-stage process of converting relatively objective sensory input (e.g., light, sound) into a subjectively meaningful experience. *A
content format Content or contents may refer to: Media * Content (media), information or experience provided to audience or end-users by publishers or media producers ** Content industry, an umbrella term that encompasses companies owning and providing mass m ...
- a specific encoding format for converting a specific type of
data Data (; ) are individual facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to experience. Standard reference works are often used ...

to
information Information is processed, organised and structured data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sense, data are a set of values of qualitative property, qualitative or quant ...

. *Text encoding uses a
markup language #REDIRECT Markup language #REDIRECT Markup language In computer text processing, a markup language is a system for annotation, annotating a document in a way that is Syntax (logic), syntactically distinguishable from the text, meaning when the do ...
to tag the structure and other features of a text to facilitate processing by computers. (See also
Text Encoding Initiative The Text Encoding Initiative (TEI) is a written language, text-centric community of practice in the List of academic disciplines, academic field of digital humanities, operating continuously since the 1980s. The community currently runs a mailing ...

.) *
Semantics encoding{{unreferenced, date=March 2017 A semantics encoding is a translation between formal language In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, str ...
of formal language A informal language B is a method of representing all terms (e.g. programs or descriptions) of language A using language B. *
Data compression In signal processing Signal processing is an electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electro ...
transforms a signal into a code optimized for
transmission Transmission may refer to: Science and technology * Power transmissionPower transmission is the movement of energy from its place of generation to a location where it is applied to perform useful Mechanical work, work. Power (physics), Power is d ...
or storage, generally done with a
codec A codec is a device or computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer program'' is a Set ...
. * Neural encoding - the way in which information is represented in
neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

s. * Memory encoding - the process of converting sensations into memories. * Television encoding:
NTSC The National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12-19, with Some supplementary references cited in the Reports, and the Petition for adoption of transm ...
,
PAL PAL 300px, upright=1.2, Analog television encoding systems by nation; SECAM.html"_;"title="NTSC_(green),_SECAM">NTSC_(green),_SECAM_(orange),_and_PAL_(blue). Phase_Alternating_Line_(PAL)_is_a_colour_encoding_system_for_Analog_television.html" ...
and
SECAM SECAM, also written SÉCAM (, ''séquentiel couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system first used in France France (), officially the French Republic (french: link=no ...

Other examples of decoding include: * *
Decoding methods In coding theory Coding theory is the study of the properties of codes and their respective fitness for specific applications. Codes are used for data compression In signal processing, data compression, source coding, or bit-rate reduction is ...
, methods in communication theory for decoding codewords sent over a noisy channel *
Digital signal processing Digital signal processing (DSP) is the use of digital processing Digital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of ...
, the study of signals in a digital representation and the processing methods of these signals *
Digital-to-analog converter In , a digital-to-analog converter (DAC, D/A, D2A, or D-to-A) is a system that converts a into an . An (ADC) performs the reverse function. There are several DAC ; the suitability of a DAC for a particular application is determined by ...
, the use of analog circuit for decoding operations * Word decoding, the use of
phonics Phonics is a method for teaching people how to read and write an alphabetic language An alphabet is a standardized set of basic written symbols or graphemes (called letter (alphabet), letters) that represent the phonemes of certain spoke ...
to decipher print patterns and translate them into the sounds of language

# Codes and acronyms

Acronym An acronym is a word In linguistics Linguistics is the scientific study of language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign langu ...
s and abbreviations can be considered codes, and in a sense, all
language A language is a structured system of communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...

s and
writing system A writing system is a method of visually representing verbal communication Communication (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communic ...
s are codes for human thought.
International Air Transport Association airport code An IATA airport code, also known as an IATA location identifier, IATA station code, or simply a location identifier, is a three-letter geocode A geocode is a code In communication Communication (from Latin ''communicare'', meaning "to ...
s are three-letter codes used to designate airports and used for
bag tag Bag tags, also known as baggage tags, baggage checks or luggage tickets, have traditionally been used by bus, train, and airline An airline is a company that provides air transport services for traveling passenger A passenger (also abb ...
s.
Station codeImage:signatur.jpg, 300px, Station code Lp for Linköping Central Station in Sweden A station code is an abbreviation used on railways for train station, railway stations. The codes are most used internally in the business, but can be seen at railwa ...
s are similarly used on railways but are usually national, so the same code can be used for different stations if they are in different countries. Occasionally, a code word achieves an independent existence (and meaning) while the original equivalent phrase is forgotten or at least no longer has the precise meaning attributed to the code word. For example, '30' was widely used in
journalism Journalism is the production and distribution of report Image:Hurt Report cover page.png, 220px, Example of a front page of a report A report is a document that presents information in an organized format for a specific audience and purpose. ...

to mean "end of story", and has been used in other contexts to signify "the end".

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Cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

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Code (semiotics) In semiotics Semiotics (also called semiotic studies) is the study of sign processes (semiosis), which are any activity, conduct, or process that involves Sign (semiotics), signs, where a sign is defined as anything that communicates a Meaning (s ...
* Equipment codes *
Quantum error correction Quantum error correction (QEC) is used in Quantum computer, quantum computing to protect quantum information from errors due to decoherence and other quantum noise. Quantum error correction is essential if one is to achieve fault-tolerant quantum ...
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Semiotics Semiotics (also called semiotic studies) is the study of sign processes (semiosis Semiosis (, ), or sign process, is any form of activity Activity may refer to: * Action (philosophy), in general * Human activity: human behavior, in sociology ...

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Universal language Universal language may refer to a hypothetical or historical language spoken and understood by all or most of the world's population. In some contexts, it refers to a means of communication said to be understood by all humans. It may be the idea ...

# References

* {{cite journal , last1=Chevance , first1=Fabienne , title=Case for the genetic code as a triplet of triplets , journal=Proceedings of the National Academy of Sciences of the United States of America , volume=114 , issue=18 , pages=4745–4750 , pmc=5422812 , year=2017 , pmid=28416671 , doi=10.1073/pnas.1614896114 , doi-access=free Encodings Signal processing