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'' value, a measure of substituent effects on the stereochemistry of cyclohexane * absorbance (''A'') * acceleration (''a'') * activity (chemistry) (''a'') * adsorption (a) * annum (a), for year * Hectare#Are, are (a), a unit of area (equal to 100 square metres; redirects to ''hectare'') * atto- (a-), the SI prefix meaning 10⁻¹⁸ * Ampere (A), unit of electric current * ångström (Å) a unit of length (equal to 1 metres) * area (''A'') * attenuation coefficient (''a'') * Bohr radius (''a''₀) * chemical affinity (''A'') * gain (electronics) (''A'') * Hall coefficient (''A''_H) * Hamaker constant (''A'') * Helmholtz free energy (''A'') * Hyperfine coupling constant (''a'' or ''A'') * magnetic vector potential (''A'') * mass number of a nuclide (''A'') * pre-exponential factor (''A'') * one of the reciprocal lattice vectors (''a*'') * relative atomic mass (''A''_r) * Richardson's constant (''A'') * rotational constant (''A'') * specific surface area (''a'') * thermal diffusivity (''a'') * unit cell length (''a'')

Astronomy

* A whitish-blue class of stars in the Morgan–Keenan system; see Stellar classification * Part of the Naming of comets, provisional designation of a comet (e.g., C/1760 A1), indicating a January 1 through 15 discovery * The semi-major axis of an orbit

Biology

* A+ and A−, human blood types * Vitamin A, also called retinol, an essential human nutrient * Haplogroup A (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup * Haplogroup A (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup * Adenine, a nucleic acid * Adenosine, 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 Sharp (Axiom), A^♯, an object-oriented functional programming language * A Sharp (.NET) (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#Anchor, HTML element for an anchor tag * a, equivalent (qname) to the RDF Schema#Properties, RDF Schema Property rdf:type * A level of web accessibility defined by the Web Content Accessibility Guidelines * The List of DNS record types, address record type of DNS, defined in RFC 1035

Mathematics and logic

* A numerical digit 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 symbolic logic (symbol ∀ or

\forall

, an inverted letter A) * Universal affirmative, one of the four types of categorical proposition in logic * Mills' constant 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 vacuum tube filament type battery * List_of_battery_sizes#Cylindrical_batteries, A battery (size), a standard battery size * Anode, an electrode * A, historical symbol for chemical element argon, 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'', 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), 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'' * ''"A" Is for Alibi'', the first novel in Sue Grafton's "Alphabet mystery" series, published in 1982 * Matthew Arnold, who used the pseudonym "A" * Isaac Asimov, who used the pseudonym "Dr. A" * Alexander Pope, who used the pseudonym "A"

Film and TV

Films

* A (1965 film), ''A'' (1965 film), a short film animated by Jan Lenica * A (1998 Kannada film), ''A'' (1998 Kannada film), an Indian movie directed by Upendra * A (1998 Japanese film), ''A'' (1998 Japanese film), a documentary film about a Buddhist sect called "A" * A (2002 film), ''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 * 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 (TV series), ''Pretty Little Liars'' *A (The Walking Dead), "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 (Spanish TV channel), Antena 3. *A, the production code for the 1963 ''Doctor Who'' serial ''An Unearthly Child''

Music

* A (musical note), the sixth solfège note * A major, a scale * A minor, a scale * A major chord; see Chord names and symbols (popular music)

Performers

* A (band), a British alternative rock band

Albums

* A (Agnetha Fältskog album), ''A'' (Agnetha Fältskog album), 2013 * A (Cass McCombs album), ''A'' (Cass McCombs album), 2003 * A (Jimmy Raney album), ''A'' (Jimmy Raney album), 1957 * A (Jethro Tull album), ''A'' (Jethro Tull album), 1980 * A (Usher and Zaytoven album), ''A'' (Usher and Zaytoven album), 2018 * ''A'', a Denki Groove album (read as "Ace") * A (Ayumi Hamasaki EP), ''A'' (Ayumi Hamasaki EP), 1999 * A (single album), ''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 (Rainbow song), "A" (Rainbow song), a 2010 single by Rainbow * "A", song by Got7 from ''Got Love (EP), Got Love'' (2014) * "A", song by the band Barenaked Ladies from ''Maybe You Should Drive'' * "A", song by Cartel from ''Chroma (album), Chroma'' * "A", a List of Dance Dance Revolution songs, song in the Dance Dance Revolution video game series, by DJ Amuro

Other media

* /a/, the anime and manga section on 4chan * 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", 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 romanized name of the Bengali letter অ * A (cuneiform), the romanized name of a cuneiform sign * A (Cyrillic) (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 (Α or α), the first letter of the Greek alphabet

Other uses in linguistics

* A and an, the indefinite article in English * List of glossing abbreviations, 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 * ''a.'', an abbreviation of ''ante'' (Latin language, Latin for "before") used in etymologies

People

* A (pharaoh), an Egyptian pharaoh * A Martinez, an American actor and singer * Matthew Arnold, who used the pseudonym "A" * Isaac Asimov, who used the pseudonym "Dr. A" * Alexander Pope, who used the pseudonym "A" * Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116, a Swedish child born in 1991, alternately called "A"

Philosophy and religion

* A, the Dominical letter of a common year starting on Sunday * Scarlet A, symbol for atheism adopted by the Out Campaign, a public awareness initiated by Elizabeth Cornwell and Richard Dawkins * Alpha, (sometimes A) in Christian theology, a metaphor for the beginning/creation of time and matter * An Anarchist symbolism, anarchist symbol, 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) ** Ford Model A (1927–31) * Geometry A, an electric mid-size sedan by Geely Auto

Rail

* A (S-train) a service on the S-train network in Copenhagen * Line A (Buenos Aires Underground), Line A of the Buenos Aires Subte * Line A (Prague Metro) * NZR A class (disambiguation) 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, British 0-4-4T steam locomotives introduced in 1875 ** LD&ECR Class A, British 0-6-2T steam locomotives introduced in 1895 ** LNWR Class A, British 0-8-0 steam locomotives introduced in 1893 ** NER Class A, British 2-4-2T steam locomotives introduced in 1886 ** SER A class, British 4-4-0 steam locomotives introduced in 1879 ** Taff Vale Railway A class, British 0-6-2T steam locomotives introduced in 1914

Ships

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

Other uses

* A (grade), an academic grade * A series of paper sizes defined by ISO 216, e.g. A4, A5 sizes * A formation, an American football offensive formation * A-Frame, a type of structure * Ace, 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 * List of military time zones#A, Alfa, the military time zone code for UTC+01:00 * Farmall A, a tractor produced by International Harvester from 1939 to 1947