AO

AO may stand for:

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• Aosta Valley (Vallée d'Aoste, Valle d'Aosta), abbreviation for the region and province of Italy
• Oiler, US Navy hull classification symbol (AO)
• Adults Only, contents rated not suitable for people under 18 by Entertainment Software Rating Board
• Anarchy Online, a science fiction Massive(ly) multiplayer online role-playing game
• the ISO 3166-1 alpha-2 country code for Angola
• the IATA code for Australian Airlines
• Arctic oscillation
• The postnominal letters of an Officer of the Order of Australia

See also: A0 (A-zero)

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