Fidelity is the quality of

faithfulness Faithfulness means unfailingly remaining loyal to someone or something, and putting that loyalty into consistent practice regardless of extenuating circumstances. It may be exhibited, for example, by a husband or wife who does not engage in se ...

loyalty Loyalty is a Fixation (psychology), devotion to a country, philosophy, group, or person. Philosophers disagree on what can be an object of loyalty, as some argue that loyalty is strictly interpersonal and only another human being can be the obj ...

. Its original meaning regarded

duty A duty (from "due" meaning "that which is owing"; , past participle of ; , whence "debt") is a commitment or expectation to perform some action in general or if certain circumstances arise. A duty may arise from a system of ethics or morality, e ...

in a broader sense than the related concept of ''

fealty An oath of fealty, from the Latin (faithfulness), is a pledge of allegiance of one person to another. Definition In medieval Europe, the swearing of fealty took the form of an oath made by a vassal, or subordinate, to his lord. "Fealty" also r ...

''. Both derive from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word , meaning "faithful or loyal". In the

City of London The City of London, also known as ''the City'', is a Ceremonial counties of England, ceremonial county and Districts of England, local government district with City status in the United Kingdom, city status in England. It is the Old town, his ...

financial markets it has traditionally been used in the sense encompassed in the motto "my word is my bond".

In moral philosophy

In moral philosophy, fidelity refers to a person who keeps agreements. Strong fidelity refers to a person who keeps agreements even if not mutually beneficial to the other person.

Audio and electronics

In audio, "fidelity" denotes how accurately a copy reproduces its source. In the 1950s, the terms "

high fidelity High fidelity (hi-fi or, rarely, HiFi) is the high-quality reproduction of sound. It is popular with audiophiles and home audio enthusiasts. Ideally, high-fidelity equipment has inaudible noise and distortion, and a flat (neutral, uncolored) ...

" or "hi-fi" were popularized for equipment and recordings which exhibited more accurate

sound reproduction Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording t ...

. For example, a worn

gramophone record A phonograph record (also known as a gramophone record, especially in British English) or a vinyl record (for later varieties only) is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The g ...

will have a lower fidelity than one in good condition, and a recording made by a low budget record company in the early 20th century is likely to have significantly less audio fidelity than a good modern recording. Similarly in

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, fidelity refers to the correspondence of the output signal to the input signal, rather than sound quality, as in the popular internet connection technology "

Wi-Fi Wi-Fi () is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital devices to exchange data by ...

". The term "

lo-fi Lo-fi (also typeset as lofi or low-fi; short for low fidelity) is a music or production quality in which elements usually regarded as imperfections in the context of a recording or performance are present, sometimes as a deliberate stylistic ch ...

" has existed since at least the 1950s, shortly after the acceptance of "hi-fi", but its definition evolved continuously between the 1970s and 2000s. In the 1976 edition of the ''Oxford Dictionary'', lo-fi was added under the definition of "sound production less good in quality than '

hi-fi High fidelity (hi-fi or, rarely, HiFi) is the high-quality reproduction of sound. It is popular with audiophiles and home audio enthusiasts. Ideally, high-fidelity equipment has inaudible noise and distortion, and a flat (neutral, uncolored) ...

'", and in the glossary of the 1977 book ''The Tuning of the World'', was defined as "unfavourable signal-to-noise ratio". In 2003, the ''Oxford Dictionary'' added a second definition: "A genre of rock music characterized by minimal production, giving a raw and unsophisticated sound." A third was added in 2008: "Unpolished, amateurish, or technologically unsophisticated, esp. as a deliberate aesthetic choice."

Scientific modelling and simulation

In the fields of

scientific modelling Scientific modelling is an activity that produces models representing empirical objects, phenomena, and physical processes, to make a particular part or feature of the world easier to understand, define, quantify, visualize, or simulate. It ...

and

simulation A simulation is an imitative representation of a process or system that could exist in the real world. In this broad sense, simulation can often be used interchangeably with model. Sometimes a clear distinction between the two terms is made, in ...

, fidelity refers to the degree to which a model or simulation reproduces the state and behaviour of a real world object, feature or condition. Fidelity is therefore a measure of the realism of a model or simulation. Simulation fidelity has also been described in the past as "degree of similarity". In quantum mechanics and optics, the fidelity of a field is calculated as an overlap integral of the field of interest with a reference or target field.

Program evaluation

In the field of

program evaluation Program evaluation is a systematic method for collecting, analyzing, and using information to answer questions about projects, policies and programs, particularly about their effectiveness and efficiency. In the public, private, and voluntar ...

, the term fidelity denotes how closely a set of procedures were implemented as they were supposed to have been. For example, it is difficult to draw conclusions from a study about formative assessment in school classrooms if the teachers are not able or willing to follow the procedures they received in training.

Translation

translation Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...

, ''fidelity'' is the extent to which a translation accurately renders the meaning of the source text, without distortion. It is contrasted with ''transparency'', which is the extent to which a translation appears to a native speaker of the target language to have originally been written in that language.

References