View source for A (disambiguation)

{{distinguish|Å (disambiguation)}}
{{wiktionary|A}}
'''[[A]]''' is the first letter of the Latin and English alphabet.

'''A''' may also refer to:
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== 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<sup>−18</sup>
* [[Ampere]] (A), unit of electric current
* [[ångström]] (Å) a unit of length (equal to 1{{e|−10}} metres)
* [[area]] (''A'')
* [[attenuation coefficient]] (''a'') 
* [[Bohr radius]] (''a''<sub>0</sub>) 
* [[chemical affinity]] (''A'')
* [[gain (electronics)]] (''A'')
* [[Hall coefficient]] (''A''<sub>H</sub>)
* [[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 vector]]s  (''a*'')
* [[relative atomic mass]] (''A''<sub>r</sub>)
* [[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 type]]s
* [[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

=== Computing ===
====Programming languages====
* [[A+ (programming language)]]
* [[A Sharp (Axiom)|A<sup>♯</sup>]], 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
* {{tag|a|content=}}, 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 (<math>\mathbb{A}</math>) (U+1D538 in Unicode)
* [[Universal quantifier]] in symbolic logic (symbol ∀ or <math>\forall</math>, 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===
{{for|vehicles|#Transport}}
* [[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 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]]''
*[[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! (album)|''A!'' (album)]], by Alexa Feser, 2019
* [[A' (album)|''A''' (album)]], by Afrirampo, 2004

====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 A from ''[['A' vs. Monkey Kong]]''
* "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===
* <code>/a/</code>, 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 (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
* [[List of glossing abbreviations|A]], a glossing abbreviation for agent-like argument of canonical transitive verb
* {{IPA|a}}, the IPA representation of the [[open front unrounded vowel]]
* {{IPA|ɑ}}, 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 initiative proposed 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
* The Gregory-Aland siglum for the [[Codex Alexandrinus]].

== 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)]]
* [[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 [[File:Toei Asakusa line symbol.svg|17px]]
* The official West Japan Railway Company service symbol for:
** [[File:JRW kinki-A.svg|17px]] [[Akō Line]], [[Biwako Line]], [[JR Kobe Line|Kobe Line]], [[JR Kyoto Line|Kyoto Line]], [[Hokuriku Main Line]], [[San'yō Main Line]], and [[Tōkaidō Main Line|JR West Tōkaidō Line]].
** [[File:JRW san-A.svg|17px]] [[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)|''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
* {{SMS|A}}, a Kaiserliche Marine tanker

=={{Anchor|Other}}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
* [[Aalto University]], public research university in Espoo, Finland
* [[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
* [[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
* [[Oakland A's]], or the Athletics, a professional baseball team based in Oakland, California, United States

==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)]]

{{disambiguation}}