A (disambiguation)

A is the first letter of the Latin and English alphabet, but its significance goes beyond being a mere letter. In this comprehensive article, we explore the various meanings and references associated with the letter A.

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 (A): a measure of the amount of light absorbed by a substance.
• acceleration (a): the rate of change of velocity.
• activity (chemistry) (a): a measure of the effective concentration of a solute in a solution.
• adsorption (a): the process of molecules adhering to the surface of a solid.
• annum (a): a unit of time equal to one year.
• are (a): a unit of area equal to 100 square meters.
• atto- (a-): the SI prefix representing 10^-18.
• Ampere (A): a unit of electric current.
• ångström (Å): a unit of length equal to 1×10^-10 meters.
• area (A): the extent or measurement of a surface.
• attenuation coefficient (a): a measure of how a material attenuates or weakens a beam of energy.
• Bohr radius (a0): a physical constant that represents the size of the hydrogen atom.
• chemical affinity (A): the attraction or force between atoms or molecules.
• gain (electronics) (A): the amplification factor of an electronic device.
• Hall coefficient (AH): a parameter that characterizes the behavior of electric currents in solid-state materials.
• Hamaker constant (A): a parameter used to describe the attractive forces between particles or surfaces.
• Helmholtz free energy (A): a thermodynamic potential that describes the work that can be extracted from a system at a constant temperature and volume.
• Hyperfine coupling constant (a or A): a parameter that characterizes the interaction between the magnetic moments of electrons and nuclei.
• magnetic vector potential (A): a vector field that represents the magnetic potential energy of a magnetic field.
• mass number of a nuclide (A): the total number of protons and neutrons in an atomic nucleus.
• pre-exponential factor (A): a coefficient used in the Arrhenius equation to describe the temperature dependence of reaction rates.
• *reciprocal lattice vectors (a)**: vectors that describe the reciprocal lattice of a crystal.
• relative atomic mass (Ar): the average mass of an element's isotopes relative to the mass of carbon-12.
• Richardson's constant (A): a fundamental physical constant that relates the current density to the temperature and work function of a metal.
• rotational constant (A): a parameter that characterizes the rotational energy levels of a molecule.
• specific surface area (a): the surface area per unit mass of a material.
• thermal diffusivity (a): a measure of how quickly heat diffuses through a material.
• unit cell length (a): the length of a unit cell in a crystal lattice.

Astronomy

• A: a whitish-blue class of stars in the Morgan-Keenan system, representing one of the stellar classifications.
• A: part of the provisional designation of a comet, indicating a January 1 through 15 discovery.
• A: the semi-major axis of an orbit.

Biology

• A+ and A-: human blood types.
• Vitamin A: also known as retinol, an essential human nutrient.
• Haplogroup A (mtDNA): a human mitochondrial DNA haplogroup.
• Haplogroup A (Y-DNA): a Y-chromosomal DNA haplogroup.
• Adenine: a nucleic acid.
• Adenosine: a nucleoside.
• A (or Ala): an abbreviation for the amino acid alanine.
• ATC code A: Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System.

Computing

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.
• <a></a>: 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: a numerical digit representing ten in hexadecimal and other positional numeral systems with a radix of 11 or greater.
• A: sometimes represented in blackboard bold, it represents the algebraic numbers.
• Universal quantifier: represented by the symbol ∀ or ∀, an inverted letter A in symbolic logic.
• Universal affirmative: one of the four types of categorical proposition in logic.
• Mills' constant: represented by the symbol A.
• Glaisher-Kinkelin constant: 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 the chemical element argon.
• The center of a hexagonal face of the Brillouin zone: in physics.

Arts and Media

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 (The Scarlet Letter): the titular letter in the novel The Scarlet Letter.
• "A Is for Alibi": the first novel in Sue Grafton's "Alphabet mystery" series.
• Authors who used the pseudonym "A": Matthew Arnold, Isaac Asimov, and Alexander Pope.

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.
• A: a British Board of Film Classification rating used from 1912 to 1982.

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: the 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 musical scale.
• A minor: a musical scale.
• A major chord: a chord commonly used in 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 (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": a song by A from 'A' vs. Monkey Kong.
• "A": a song by Got7 from Got Love (2014).
• "A": a song by the band Barenaked Ladies from Maybe You Should Drive.
• "A": 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.
• A: a Japanese video game rating in the Computer Entertainment Rating Organization suitable for all ages.

Geography

• Austria: represented on the vehicle registration plates of the European Union.
• "The A": a nickname for the U.S. city of Atlanta, Georgia.

Linguistics

Letters

• 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): the first letter of the Cyrillic alphabet.
• A (kana): the romanized name of the Hiragana syllable letter あ and 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 the agent-like argument of a canonical transitive verb.
• 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.

People

• A (pharaoh): an Egyptian pharaoh.
• A Martinez: an American actor and singer.
• Authors who used the pseudonym "A": Matthew Arnold, Isaac Asimov, and Alexander Pope.
• 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 initiative by Elizabeth Cornwell and Richard Dawkins.
• Alpha: sometimes represented as A in Christian theology, a metaphor for the beginning/creation of time and matter.
• Anarchy symbol: an A within a circle, representing anarchism.

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 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 A.
• Official West Japan Railway Company service symbol for:
  • Akō Line, Biwako Line, Kobe Line, Kyoto Line, Hokuriku Main Line, San'yō Main Line, and JR West Tōkaidō Line.
  • 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

• M/Y A (motor yacht): a 119m yacht owned by Andrey Melnichenko.
• S/Y A (sailing yacht): 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.

See also

• Å (disambiguation).
• ⓐ and Ⓐ: see Enclosed Alphanumerics.
• Class A (disambiguation).
• Model A (disambiguation).
• Circled a (disambiguation).
• Single-A: or Class A, a classification of minor league baseball.
• A band (disambiguation).
• A class (disambiguation).
• A type (disambiguation).
• Aleph (disambiguation).
• Alpha (disambiguation).
• A1 (disambiguation).
• AA (disambiguation).
• AAA (disambiguation).
• AAAA (disambiguation).

Image Caption: This image represents the letter "A" in various contexts.