A is the first letter of the Latin and English alphabet. A may also refer to:

Science and technology

Quantities and units

* ''a'', a measure for the attraction between particles in the Van der Waals equation * ''A'' value, a measure of substituent effects on the stereochemistry of cyclohexane *

absorbance Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". Alternatively, for samples which scatter light, absorbance may be defined as "the negative lo ...

(''A'') *

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the ...

(''a'') * activity (chemistry) (''a'') *

adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...

(a) * annum (a), for year *

are Are commonly refers to: * Are (unit), a unit of area equal to 100 m2 Are, ARE or Åre may also refer to: Places * Åre, a locality in Sweden * Åre Municipality, a municipality in Sweden **Åre ski resort in Sweden * Are Parish, a municipa ...

(a), a unit of area (equal to 100 square metres; redirects to ''hectare'') *

atto- A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The pre ...

(a-), the SI prefix meaning 10⁻¹⁸ *

Ampere The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...

(A), unit of electric current * ångström (Å) a unit of length (equal to 1 metres) *

area Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape A shape or figure is a graphics, graphical representation of an obje ...

(''A'') * attenuation coefficient (''a'') * Bohr radius (''a''₀) * chemical affinity (''A'') *

gain (electronics) In electronics, gain is a measure of the ability of a two-port electrical network, circuit (often an amplifier) to increase the Electric power, power or amplitude of a Signal (electrical engineering), signal from the input to the output port by a ...

(''A'') * Hall coefficient (''A''_H) * Hamaker constant (''A'') *

Helmholtz free energy In thermodynamics, the Helmholtz free energy (or Helmholtz energy) is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal In thermodynamics, an isotherma ...

(''A'') *

Hyperfine coupling constant Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but the spin ...

(''a'' or ''A'') *

magnetic vector potential In classical electromagnetism, magnetic vector potential (often called A) is the vector quantity defined so that its curl is equal to the magnetic field: \nabla \times \mathbf = \mathbf. Together with the electric potential ''φ'', the magnetic v ...

(''A'') * mass number of a nuclide (''A'') * pre-exponential factor (''A'') * one of the reciprocal lattice vectors (''a*'') *

relative atomic mass Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...

(''A''_r) * Richardson's constant (''A'') * rotational constant (''A'') * specific surface area (''a'') *

thermal diffusivity In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI ...

(''a'') * unit cell length (''a'')

Astronomy

* A whitish-blue class of stars in the Morgan–Keenan system; see

Stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

* Part of the provisional designation of a comet (e.g., C/1760 A1), indicating a January 1 through 15 discovery * The

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of an orbit

Biology

* A+ and A−, human

blood type A blood type (also known as a blood group) is a classification of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrate ...

s *

Vitamin A Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...

, also called retinol, an essential human nutrient *

Haplogroup A (mtDNA) In human mitochondrial genetics, Haplogroup A is a human mitochondrial DNA (mtDNA) haplogroup. Origin Haplogroup A is believed to have arisen in Asia some 30,000–50,000 years BC. Its ancestral haplogroup was Haplogroup N. However, the exta ...

, a human mitochondrial DNA (mtDNA) haplogroup *

Haplogroup A (Y-DNA) Haplogroup A is a human Y-chromosome DNA haplogroup, which includes all living human Y chromosomes. Bearers of extant sub-clades of haplogroup A are almost exclusively found in Africa (or among descendants of populations which have recently le ...

, a Y-chromosomal DNA (Y-DNA) haplogroup *

Adenine Adenine () ( symbol A or Ade) is a nucleobase (a purine derivative). It is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The three others are guanine, cytosine and thymine. Its derivati ...

, a nucleic acid *

Adenosine Adenosine ( symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9-glycosidic bond. Adenosine is one of the four nucleoside building ...

, a nucleoside * Alanine, an amino acid * ATC code A, Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System

Computing

Programming languages

A+ (programming language) A+ is a high-level, interactive, interpreted array programming language designed for numerically intensive applications, especially those found in financial applications. History In 1985, Arthur Whitney created the A programming language to ...

* A^♯, an object-oriented functional programming language *

A Sharp (.NET) A# is a port of the Ada programming language to the Microsoft .NET platform. A# is freely distributed by the Department of Computer Science at the United States Air Force Academy as a service to the Ada community under the terms of the GNU Ge ...

(also written "A#"), a port of Ada to the Microsoft .NET Platform * BASIC A+

Other uses in computing

* A* search algorithm, a pathfinding algorithm * A-0 System, an early computer compiler * , the HTML element for an anchor tag * a, equivalent (qname) to the RDF Schema Property rdf:type * A level of web accessibility defined by the Web Content Accessibility Guidelines * The address record type of DNS, defined in RFC 1035

Mathematics and logic

* A

numerical digit A numerical digit (often shortened to just digit) is a single symbol used alone (such as "2") or in combinations (such as "25"), to represent numbers in a positional numeral system. The name "digit" comes from the fact that the ten digits (Latin ...

meaning ten in hexadecimal and other positional numeral systems with a radix of 11 or greater * Sometimes in blackboard bold represents the algebraic numbers (

\mathbb

) (U+1D538 in Unicode) *

Universal quantifier In mathematical logic, a universal quantification is a type of quantifier, a logical constant which is interpreted as "given any" or "for all". It expresses that a predicate can be satisfied by every member of a domain of discourse. In other w ...

in symbolic logic (symbol ∀ or

\forall

, an inverted letter A) * Universal affirmative, one of the four types of

categorical proposition In logic, a categorical proposition, or categorical statement, is a proposition that asserts or denies that all or some of the members of one category (the ''subject term'') are included in another (the ''predicate term''). The study of arguments ...

in logic *

Mills' constant In number theory, Mills' constant is defined as the smallest positive real number ''A'' such that the floor function of the double exponential function : \lfloor A^ \rfloor is a prime number for all natural numbers ''n''. This constant is named ...

is represented by the symbol ''A'' * Glaisher–Kinkelin constant is also often represented by the symbol ''A''

Other uses in science and technology

A battery A generic triode vacuum tube circuit showing "A", "B" and "C" batteries">vacuum_tube.html" ;"title="triode vacuum tube">triode vacuum tube circuit showing "A", "B" and "C" batteries In the early days of electronics, vacuum tube (called ''valves' ...

, a vacuum tube filament type battery * A battery (size), a standard battery size *

Anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

, an electrode * A, historical symbol for chemical element

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

, currently Ar * The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics

Arts and media

Books

* "A", a major poem by twentieth century author Louis Zukofsky * ''

a, A Novel ''a, A Novel'' is a 1968 book by the American artist Andy Warhol published by Grove Press. It is a nearly word-for-word transcription of tapes recorded by Warhol and Ondine over a two-year period in 1965–1967. The Novel ''a, A Novel'', Warh ...

'', by twentieth century artist Andy Warhol * A, the name of the Fourth Raikage, the leader of Kumogakure in the Naruto manga series * A (''Pretty Little Liars''), the main antagonist in the ''Pretty Little Liars'' book and TV series * A (for "adultery"), the titular letter in the novel ''

The Scarlet Letter ''The Scarlet Letter: A Romance'' is a work of historical fiction Historical fiction is a literary genre in which the plot takes place in a setting related to the past events, but is fictional. Although the term is commonly used as a synonym ...

'' * ''

"A" Is for Alibi ''"A" Is for Alibi'' by Sue Grafton, published by Holt McDougal, Holt, Rinehart and Winston in 1982, is the first mystery novel in the author's "Alphabet" series. Featuring sleuth Kinsey Millhone, it is set in the southern California city of Santa ...

'', the first novel in Sue Grafton's "Alphabet mystery" series, published in 1982 * Matthew Arnold, who used the pseudonym "A" *

Isaac Asimov yi, יצחק אזימאװ , birth_date = , birth_place = Petrovichi, Russian SFSR , spouse = , relatives = , children = 2 , death_date = , death_place = Manhattan, New York City, U.S. , nationality = Russian (1920–1922)Soviet (192 ...

, who used the pseudonym "Dr. A" *

Alexander Pope Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...

, who used the pseudonym "A"

Film and TV

Films

* ''A'' (1965 film), a short film animated by Jan Lenica * ''A'' (1998 Kannada film), an Indian movie directed by Upendra * ''A'' (1998 Japanese film), a documentary film about a Buddhist sect called "A" * ''A'' (2002 film), a British documentary film

Film ratings

* A, a rating in India's Central Board of Film Certification * A certificate, a film rating used by the

Canadian motion picture rating system Motion picture ratings in Canada are mostly a provincial responsibility, and each province has its own legislation regarding exhibition and admission. For home video purposes, a single Canadian Home Video Rating System rating consisting of an av ...

* A, a British Board of Film Classification rating used from 1912 to 1982, see History of British film certificates

Television

* CTV 2, a Canadian television system formerly known as A-Channel and A *A, the main antagonist and unknown character of the show ''Pretty Little Liars'' * "A" (''The Walking Dead''), an episode of the television series ''The Walking Dead'' *A, code name of Ange, the main protagonist of the anime show '' Princess Principal'' *"A"-logo for the Spanish network

Antena 3 Antena 3 may refer to: * Antena 3 (Portugal), a national radio channel produced by the Portuguese public broadcasting entity Rádio e Televisão de Portugal *Antena 3 (Romania), a Romanian television channel owned by Intact Media Group *Antena 3 (Sp ...

. *A, the production code for the 1963 ''Doctor Who'' serial '' An Unearthly Child''

Music

* A (musical note), the sixth solfège note *

A major A major (or the key of A) is a major scale based on A, with the pitches A, B, C, D, E, F, and G. Its key signature has three sharps. Its relative minor is F-sharp minor and its parallel minor is A minor. The key of A major is the only k ...

, a scale *

A minor A minor is a minor scale based on A, with the pitches A, B, C, D, E, F, and G. Its key signature has no flats and no sharps. Its relative major is C major and its parallel major is A major. The A natural minor scale is: : Changes ...

, a scale * A major chord; see Chord names and symbols (popular music)

Performers

A (band) A is a British alternative rock band from Suffolk, England, which formed in 1993. They have released 4 studio and 2 live albums, including their debut ''How Ace Are Buildings'' and the UK top 20 album ''Hi-Fi Serious''. Single releases have al ...

, a British alternative rock band

Albums

* ''A'' (Agnetha Fältskog album), 2013 * ''A'' (Cass McCombs album), 2003 * ''A'' (Jimmy Raney album), 1957 * ''A'' (Jethro Tull album), 1980 * ''A'' (Usher and Zaytoven album), 2018 * ''A'', a

Denki Groove is a Japanese music group founded in 1989. It consists of Takkyu Ishino and Pierre Taki. History Denki Groove was founded in 1989 by Takkyu Ishino and Pierre Taki, both of whom are natives of Shizuoka, Shizuoka Prefecture. The group's major-lab ...

album (read as "Ace") * ''A'' (Ayumi Hamasaki EP), 1999 * ''A'' (single album), a 2015 single by the Korean band Big Bang * A!, Alexa Feser 2019 * A' (album), an album by Afrirampo

Songs

* A or Side A, the top or first side of a

gramophone record A phonograph record (also known as a gramophone record, especially in British English), or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts nea ...

* "A" (Rainbow song), a 2010 single by Rainbow * "A", song by Got7 from '' Got Love'' (2014) * "A", song by the band Barenaked Ladies from ''

Maybe You Should Drive ''Maybe You Should Drive'' (commonly abbreviated MYSD) is the second studio album by Barenaked Ladies. It was released in August 1994 and went double platinum in Canada, reaching No. 3 upon its release. It was also their first album to chart in ...

'' * "A", song by Cartel from '' Chroma'' * "A", a song in the Dance Dance Revolution video game series, by DJ Amuro

Other media

* /a/, the anime and manga section on

4chan 4chan is an anonymous English-language imageboard website. Launched by Christopher "moot" Poole in October 2003, the site hosts boards dedicated to a wide variety of topics, from anime and manga to video games, cooking, weapons, television, ...

* A, a Japanese video game rating in the Computer Entertainment Rating Organization suitable for all ages.

Geography

* Austria, on the vehicle registration plates of the European Union *"

The A ''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...

", a nickname for the U.S. city of Atlanta, Georgia

Linguistics

Letters

* A (or a), the first letter of the Latin alphabet *

A (Bengali) The Bengali script or Bangla alphabet ( bn, বাংলা বর্ণমালা, ''Bangla bôrṇômala'') is the alphabet used to write the Bengali language based on the Bengali-Assamese script, and has historically been used to w ...

, the romanized name of the Bengali letter অ *

A (cuneiform) The cuneiform sign 𒀀 ( DIŠ, DIŠ OVER DIŠ) for a, and in the ''Epic of Gilgamesh'' the sumerogram A, Akkadian for ''mû'', "water", which is used in the ''Gilgamesh flood myth'', Chapter XI of the Epic, or other passages. The sign is ...

, the romanized name of a cuneiform sign *

A (Cyrillic) А (А а; italics: ) is a letter of the Cyrillic script. It commonly represents an open central unrounded vowel , halfway between the pronunciation of in "cat" and "father". The Cyrillic letter А is romanized using the Latin letter A ...

(A or а), the first letter of the Cyrillic alphabet * A (kana) (or a), the romanized name of the Hiragana syllable letter あ and of the Katakana syllable letter ア used in Japanese, which may also be used to represent Asia *

Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...

(Α or α), the first letter of the Greek alphabet

Other uses in linguistics

* A and an, the indefinite article in English * A, a glossing abbreviation for agent-like argument of canonical transitive verb * , the IPA representation of the open front unrounded vowel * , the IPA representation of the

open back unrounded vowel The open back unrounded vowel, or low back unrounded vowel, is a type of vowel sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is A. The l ...

* ''a.'', an abbreviation of ''ante'' (

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "before") used in etymologies

People

A (pharaoh) A was the name of a Early Dynastic pharaoh of Ancient Egypt. His name is known from a graffito serekh carved into a sandstone outcropping 10 to 12 kilometers southwest of Umm el-Dabadib at the Kharga Oasis in the Western Desert. The presence o ...

, an Egyptian pharaoh * A Martinez, an American actor and singer * Matthew Arnold, who used the pseudonym "A" *

, who used the pseudonym "Dr. A" *

, who used the pseudonym "A" *

Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116 The naming law in Sweden ( sv, lag om personnamn) is a Swedish law which requires the approval of the government agency for names to be given to Swedish children. The parents must submit the proposed name of a child within three months of birth ...

, a Swedish child born in 1991, alternately called "A"

Philosophy and religion

* A, the Dominical letter of a

common year starting on Sunday A common year starting on Sunday is any non-leap year (i.e. a year with 365 days) that begins on Sunday, January 1, 1 January, and ends on Sunday, December 31, 31 December. Its dominical letter hence is A. The most recent year was 2017 and the next ...

* Scarlet A, symbol for atheism adopted by the

Out Campaign The Out Campaign is a public awareness initiative for freethought and atheism in the US. It was initiated by Robin Elisabeth Cornwell, and is endorsed by Richard Dawkins, a prominent atheist. The campaign aims to create more openness about being an ...

, a public awareness initiated by Elizabeth Cornwell and Richard Dawkins * Alpha, (sometimes A) in

Christian theology Christian theology is the theology of Christianity, Christian belief and practice. Such study concentrates primarily upon the texts of the Old Testament and of the New Testament, as well as on Christian tradition. Christian theology, theologian ...

, a metaphor for the beginning/creation of time and matter * An

anarchist symbol Anarchists have employed certain symbols for their cause, including most prominently the circle-A and the black flag. Anarchist cultural symbols have been prevalent in popular culture since around the turn of the 21st century, concurrent wit ...

, an A within a circle

Transport

Automobile

* Ford Model A, a name used by two separate cars produced by the Ford Motor Company: **

Ford Model A (1903–04) The original Ford Model A is the first car produced by the Ford Motor Company, beginning production in 1903. Ernest Pfennig, a Chicago dentist, became the first owner of a Model A on July 23, 1903; 1,750 cars were made from 1903 through 1904 duri ...

** Ford Model A (1927–31) * Geometry A, an electric mid-size sedan by Geely Auto

Rail

A (S-train) A is a service on the S-train network in Copenhagen. It is one of the base services on the network, running every 20 minutes from about 5:00 to 0:30 every day, and every 10 minutes from about 6:15 to 19:00. It runs between Hundige and Hillerød, ...

a service on the S-train network in Copenhagen * Line A of the Buenos Aires Subte *

Line A (Prague Metro) Line A () is a line of the Prague Metro, serving the Czech capital. Chronologically the second line in the system, it was first opened in 1978 and has expanded mostly during the 1980s. With the opening of the extension to Nemocnice Motol on 6 ...

NZR A class (disambiguation) NZR A class may refer to: * NZR A class (1873); 14 tank locomotives * NZR A class (1906) The NZR A class were a class of steam locomotives built in 1906 with a 4-6-2 wheel arrangement for the New Zealand Railways Department (NZR). The class sho ...

two New Zealand steam locomotive classes * United States ** A (Los Angeles Railway) ** A (New York City Subway service), also known as the "A Eighth Avenue Express" ** Alton Railroad (reporting mark) ** A Line (Los Angeles Metro) * Britain **

LCDR A class The LCDR A class was a class of 0-4-4T steam locomotives of the London, Chatham and Dover Railway. The class was designed by William Kirtley and introduced in 1875. The A1 and A2 classes were similar, but had larger driving wheels. The differe ...

, British 0-4-4T steam locomotives introduced in 1875 **

LD&ECR Class A The LD&ECR class A (LNER Class N6) was a class of 0-6-2T steam locomotives of the Lancashire, Derbyshire and East Coast Railway. An initial batch of eight was ordered and built in 1895. An order for 15 more was placed in 1899 but five of these ...

, British 0-6-2T steam locomotives introduced in 1895 **

LNWR Class A The London and North Western Railway (LNWR) Class A was a class of 0-8-0 steam locomotives. From 1893 to 1900, Crewe Works built 111 of these engines, which had a three-cylinder compound locomotive, compound arrangement, and were designed by Fr ...

, British 0-8-0 steam locomotives introduced in 1893 **

NER Class A The NER Class A (LNER Class F8) was a class of 2-4-2 tank locomotives designed by Thomas William Worsdell and built at Gateshead works for the North Eastern Railway (NER). Sixty locomotives were built between 1886 and 1892. At this time the c ...

, British 2-4-2T steam locomotives introduced in 1886 **

SER A class The SER A class was a class of 4-4-0 locomotives on the South Eastern Railway. History For many years the South Eastern Railway (SER) had relied upon locomotives of the 2-4-0 wheel arrangements for their semi-fast passenger services. James ...

, British 4-4-0 steam locomotives introduced in 1879 **

Taff Vale Railway A class The Taff Vale Railway A class was a class of 0-6-2T steam tank locomotives designed by J. Cameron for mixed traffic work and introduced to the Taff Vale Railway (TVR) in 1914. The A class was an enlarged version of the TVR O4 class designed ...

, British 0-6-2T steam locomotives introduced in 1914

Ships

* ''A'' (motor yacht) (M/Y ''A''), a 119m yacht owned by Andrey Melnichenko * ''A'' (sailing yacht) (S/Y ''A''), a 143m yacht owned by Andrey Melnichenko * , a Kaiserliche Marine tanker

Other uses

A (grade) This is a list of grading systems used by countries of the world, primarily within the fields of secondary education and university education, organized by continent with links to specifics in numerous entries. Africa Nigeria The choice of gr ...

, an academic grade * A series of paper sizes defined by

ISO 216 ISO 216 is an international standard for paper sizes, used around the world except in North America and parts of Latin America. The standard defines the "A", "B" and "C" series of paper sizes, including A4, the most commonly available paper size ...

, e.g. A4, A5 sizes * A formation, an American football offensive formation * A-Frame, a type of structure *

Ace An ace is a playing card, Dice, die or domino with a single Pip (counting), pip. In the standard French deck, an ace has a single suit (cards), suit symbol (a heart, diamond, spade, or club) located in the middle of the card, sometimes large a ...

, a playing card * Agilent Technologies, with U.S. ticker symbol A * Sentinel Peak (Arizona), more commonly known as "A" Mountain for the man-made rock formation in the shape of the letter * Alfa, the military time zone code for UTC+01:00 *

Farmall A The Farmall A is a small one-plow row crop tractor produced by International Harvester under the Farmall brand from 1939 to 1947. The tractor was popular for its set of innovative features in a small, affordable implement. It succeeded the Far ...

, a tractor produced by International Harvester from 1939 to 1947