A (disambiguation)

A is the first letter of the Latin alphabet.

A may also refer to:

Science

• A battery, a vacuum tube filament battery
• 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
• A+ and A-, human blood types
• Adenine, nucleic acid
• Alanine, amino acid
• Adenosine, nucleoside
• ATC code A, Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System
• Anode, an electrode
• The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics
• The letter "A" was formerly the chemical symbol for the element argon, which is now indicated by the symbol Ar.

Astronomy

• A whitish-blue class of stars in the Morgan–Keenan system, see stellar classification
• A January 1 through 15 discovery in the provisional designation of a comet (for example, C/1760 A1)
• The semi-major axis of an orbit

Abbreviations for physical and chemical quantities and units

• acceleration (a)
• the unique, or one of the, reciprocal lattice vector(s) (a*)
• attenuation coefficient (a)
• activity (chemistry) (a)
• specific surface area (a)
• thermal diffusivity (a)
• unit cell length (a)
• Bohr radius (a₀)
• 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
• a', a measure for the attraction between particles in the Van der Waals equation
• magnetic vector potential (A)
• absorbance (A)
• area (A)
• A value (A), a measure of substituent effects on the stereochemistry of cyclohexane
• Helmholtz free energy (A)
• mass number (A)
• pre-exponential factor (A)
• rotational constant (A)
• Hall coefficient (A_H)
• relative atomic mass (A_r)
• ampere (A), the SI base unit of electric current
• ångström (Å), a unit of length equal to 1×10⁻¹⁰ metres
• chemical affinity (A)
• gain (electronics) (A)
• Hamaker constant (A)
• hyperfine coupling constant (a or A)
• Richardson's constant (A)

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

Computing

• A*, a pathfinding algorithm
• A-0 System, early computer compiler
• A+ (programming language)
• A^♯, the object-oriented functional programming language distributed as a separable component of Version 2 of the Axiom computer algebra system
• /a/, the anime and manga section on 4chan
• BASIC A+
• <a></a>, the HTML element for an anchor tag
• a, equivalent (qname) to the RDF Schema Property rdf:type
• A# (a port of Ada to the Microsoft .NET Platform)
• The most basic of the three levels of web site accessibility measured by Web Content Accessibility Guidelines
• The address record type of DNS defined in RFC 1035

The arts

Music

• A (musical note), the sixth solfège note
• A (band), a British rock band
• A (Agnetha Fältskog album)
• A (Cass McCombs album)
• A (Jimmy Raney album)
• A (Jethro Tull album)
• A, a Denki Groove album (read as "Ace")
• "A" (EP), an EP by Ayumi Hamasaki
• "A", song by 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
• A or Side A, the top or first side of a gramophone record
• A (Rainbow song) a single by Rainbow

Literature

• "A", major poem by twentieth century author Louis Zukofsky
• 'A', pseudonym of Matthew Arnold
• 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, the main antagonist in the Pretty Little Liars series
• A (for "adultery"), the titular letter in the novel The Scarlet Letter
• A, pseudonym of Alexander Pope
• Dr. A, pseudonym of Isaac Asimov

Film

• A (1965 film), a short film animated by Jan Lenica
• A (1998 Indian film), a Kannada 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 1912–1982, see History of British film certificates

Television

• A!, a common internet abbreviation for Animaniacs
• CTV Two, 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

Geography

• Austria, on the vehicle registration plates of the European Union
• "The A", a nickname for Atlanta, Georgia

Linguistics

• A and an, the indefinite article in English
• A, the agent-like argument of canonical transitive verb
• A (or a), the first letter of the Latin alphabet
• A (Cyrillic) (A or а), the first letter of the Cyrillic alphabet
• Alpha (Α or α), the first letter of the Greek 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
• a, the IPA representation of the open front unrounded vowel
• ɑ, the IPA representation of the open back unrounded vowel
• a., an abbreviation of ante (Latin for "before") used in etymologies

Transport

• A (New York City Subway service), also known as the "A Eighth Avenue Express"
• A (S-train) a service on the S-train network in Copenhagen
• Alton Railroad (reporting mark)
• Line A (Prague Metro)
• 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)
• NZR A class (disambiguation) two New Zealand steam locomitive classes

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

• A-Frame, a type of structure
• A, the alternate name for Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116, a Swedish child born in 1991
• Agilent Technologies, with U.S. ticker symbol A
• Anarchist symbolism, an A within a circle
• An ace in a deck of playing cards
• Alpha, (sometimes A) in Christian theology is a metaphor for the beginning/creation of time and matter
• A series of paper sizes defined by ISO 216, e.g. A4, A5 sizes
• A (grade), an academic grade
• Sentinel Peak (Arizona), more commonly known as "A" Mountain for the man-made rock formation in the shape of the letter
• Scarlet A, symbol for atheism adopted by the Out Campaign, a public awareness initiated by Elizabeth Cornwell and Richard Dawkins

See also

• Single-A, or Class A, a classification of minor league baseball
• Å (disambiguation)
• A band (disambiguation)
• A class (disambiguation)
• Class A (disambiguation)
• A1 (disambiguation)
• Alpha (disambiguation)
• Aleph (disambiguation)
• AA (disambiguation)
• AAAA (disambiguation)
• AAA (disambiguation)
• Type A (disambiguation)
• Model A (disambiguation)
• A-Type (disambiguation)