AO

AO may stand for:
*Adults Only, contents rated not suitable for people under 18 by Entertainment Software Rating Board
*Auxiliary oiler, US Navy hull classification symbol
*Anarchy Online, a science fiction Massive(ly) multiplayer online role-playing game
*Angola, 2-letter ISO and obsolete NATO country code
*Aosta Valley (Vallée d'Aoste, Valle d'Aosta), abbreviation for the region and province of Italy
*Arctic oscillation
*Atlas Orthogonal
*Atomic oxygen
*Australian Airlines, IATA code
*Officer of the Order of Australia, postnominal letters
*The nickname of a street basketball player named Aaron Owens.
*The nickname of Capitals winger Alexander Ovechkin.

In addition:
* "Ao" is a Japanese word meaning both 'blue' and 'green'.
* Ao - the people of north east India
* Ao - Tibeto-Burman language of the Ao people
* Ao - the Polynesian god
* Lord Ao - Fictional god in Dungeons & Dragons.

See also
* A0 (A-zero)
* .ao (the ccTLD for Angola).