A

Look up A in Wiktionary, the free dictionary.

A is the first letter of the Latin alphabet.

A may also refer to:

Science

• A 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

• The anode, a component of a vacuum tube
• The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics

Astronomy

• A whitish-blue class of stars in the Morgan-Keenan system
• A January 1 through 15 discovery, in the provisional designation of a comet (for example, C/1760 A1, the Great Comet of 1760) or asteroid
• As a comet designation prefix, indicates an object that was at first mistakenly identified as a comet, but is actually a minor planet (for example, A/2005 JM₃)
• 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
• 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 (A)
• Hamaker constant (A)
• hyperfine coupling constant (a or A), see Electron paramagnetic resonance#Hyperfine coupling
• 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 ( (U+1D538 in Unicode)
• The universal quantifier in symbolic logic (symbol ∀ or (an inverted letter A)
• 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 Sharp (Axiom), properly known as "A#"
• BASIC A+
• <a>, the HTML element for an anchor tag
• A Sharp (.NET) (A port of Ada to the Microsoft .NET Platform)
• The most basic of the three levels of web site accessibility measured by WCAG

The arts

• A (musical note), the sixth musical note
• A (Jethro Tull album), 1980 album by progressive rock band Jethro Tull
• A (band) is a rock band from Leeds, formed in 1995
• A (Cass McCombs album), 2003 album by Cass McCombs
• "A" (song), Ayumi Hamasaki's 10th single, released 1999
• A (TV system), a Canadian television system formerly known as A-Channel
• "A", song by Cartel (band)
• "A", song by the band Barenaked Ladies
• A, or "side A," refers to the top or first side of a vinyl record
• "A", major poem by 20th century author Louis Zukofsky
• a, A Novel, by 20th century artist Andy Warhol

Cinema

• A (Kannada film) is a Kannada movie directed by Upendra
• A (film) is a 1965 short animated film by Jan Lenica
• A, a rating in India's Central Board of Film Certification
• A certificate a film rating in Canada

Linguistics

• A and an, the indefinite article in English
• A (kana), the Japanese kana あ and ア which may be used to represent Asia
• A (Cyrillic), the first letter of the Cyrillic alphabet
• a, the IPA representation of the open front unrounded vowel
• ɑ, the IPA representation of the open back unrounded vowel

Sports

• Class A, a classification of Minor league baseball, commonly referred to as "Single A"

Miscellanea

• A-Frame, a type of structure
• 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)
• A, the alternate name for Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116, a Swedish child born in 1991
• "The A's", nickname for Oakland Athletics
• A, the U.S. ticker symbol for Agilent Technologies
• A within a circle, used in anarchist symbolism
• An ace in a deck of playing cards
• In Christian theology, alpha is a metaphor for the beginning/creation of time and matter. It is sometimes translated to A
• A, a song in Dance Dance Revolution Extreme
• The A series of paper sizes defined by ISO 216, the most frequently used being the A4 size.
• A (grade), an academic grade in North America

See also

• Å (disambiguation)
• A band (disambiguation)
• A class (disambiguation)
• Class A (disambiguation)
• Alpha (disambiguation)
• Aleph (disambiguation)

This disambiguation page lists articles associated with the same Latin letter. If an internal link led you here, you may wish to change the link to point directly to the intended article.