A (disambiguation)

A is the first letter of the Latin and English alphabet.

A may also refer to:

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 (A)
 * acceleration (a)
 * activity (chemistry) (a)
 * adsorption (a)
 * annum (a), for year
 * 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 (a0)
 * chemical affinity (A)
 * gain (electronics) (A)
 * Hall coefficient (AH)
 * 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 (Ar)
 * 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 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
 * A (or Ala), abbreviation for amino acid alanine
 * ATC code A, Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System

Programming languages

 * A+ (programming language)
 * 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 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 meaning ten in hexadecimal and other positional numeral systems with a radix of 11 or greater
 * Sometimes in blackboard bold represents the algebraic numbers ($$\mathbb{A}$$) (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
 * 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

Books

 * "A", a 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), 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"

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
 * 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.
 * 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), 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 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" (Rainbow song), a 2010 single by Rainbow
 * "A", song by A from 'A' vs. Monkey Kong
 * "A", song by Got7 from Got Love (2014)
 * "A", song by the band Barenaked Ladies from Maybe You Should Drive
 * "A", song by Cartel from Chroma
 * "A", a song in the Dance Dance Revolution video game series, by DJ Amuro

Other media

 * , 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

Letters

 * A (or a), the first letter of the Latin alphabet
 * A (Indic), the many form of brahmic "a"
 * 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
 * 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 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 symbol, an A within a circle

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 of the Buenos Aires Subte
 * Line A (Prague Metro)
 * Mexico City Metro Line A
 * NZR A class (disambiguation) two New Zealand steam locomotive classes
 * RER A, a line in the RER of Paris
 * Lyon Metro Line A
 * Toei Asakusa Line, a subway service operated by the Tokyo Metropolitan Bureau of Transportation (Toei), labeled Toei Asakusa line symbol.svg
 * The official West Japan Railway Company service symbol for:
 * JRW kinki-A.svg Akō Line, Biwako Line, Kobe Line, Kyoto Line, Hokuriku Main Line, San'yō Main Line, and JR West Tōkaidō Line.
 * JRW san-A.svg San'in Main Line.
 * 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) (M/Y A), a 119m yacht owned by Andrey Melnichenko
 * A (sailing yacht) (S/Y A), a 143m yacht owned by Andrey Melnichenko
 * SMS A, 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 human-made rock formation in the shape of the letter
 * Alfa, the military time zone code for UTC+01:00
 * Farmall A, a tractor produced by International Harvester from 1939 to 1947
 * Oakland A's, or the Athletics, a professional baseball team based in Oakland, California, United States