# AO

AO, aO, Ao, or ao may refer to:

## Places

* Ao (building)
* Ao, Estonia, village in Väike-Maarja Parish, Lääne-Viru County, Estonia
* Ao Line, commuter railway line in Hyōgo Prefecture, Japan
* Ao River (Fujian), in China
* Ao Station, railway station in the city of Ono, Hyōgo Prefecture, Japan
* Aodu, capital of Shang dynasty, near Zhengzhou
* Aoshima, Ehime, island in Japan
* Aoshima, Miyazaki, island in Japan
* Angola (ISO 3166-1 alpha-2 code AO)

## Arts and entertainment

* Adults Only, an entertainment rating
* AO Music (AOmusic), a world-music fusion group consisting of Jay Oliver, Miriam Stockley and others
* Ao: The Last Hunter, a 2010 prehistoric drama movie
* Eureka Seven: AO, Japanese mecha anime television series
* Lord Ao, a fictional deity in the Dungeons & Dragons universe
* Annoying Orange, an American comedy web series

## Businesses and organizations

* AO (originally American Optical Company) eyeglass lenses, a brand now merged with Carl Zeiss Vision
* AO Foundation (originally Arbeitsgemeinschaft für Osteosynthesefragen), a non-profit organisation dedicated to the treatment of trauma and disorders of the musculoskeletal system
* AO Racing, an American sports car racing team
* AO World, a UK retailer of household appliances trading under the brand name ao.com
* AO, Aktsionernoye Obschestvo or Aktsionernoye Obshchestvo (акционерное общество), a type of Russian corporate entity; see open joint-stock company
* Athletics Ontario, formally Ontario Track and Field Association (OTAF)
* Australian Airlines (IATA code AO)

## Government and politics

* Administrative Office of the United States Courts
* Administrative Officer (United Kingdom), a grade within the United Kingdom's Civil Service
* Administrative Officer (Hong Kong), a grade within the Hong Kong's Civil Service
* Autonomous oblast, type of Russian administrative division
* Autonomous okrug, type of Russian administrative division
* NSDAP/AO, Foreign Organization branch of the Nazi Party
* Officer of the Order of Australia, postnominal AO

## Military

* Area of operations, a U.S. military term
* A US Navy hull classification symbol: Fleet oiler (AO)
* AO-, the prefix for several firearms
* Aviation Ordnanceman, a United States Navy occupational rating

## Philosophy and religion

* Alpha and Omega (abbreviation)
* Ao (Māori mythology), a deity in Māori mythology
* Ao (turtle), a creature in Chinese mythology
* Ao, a type of Easter Island wood carving

## Science and technology

* (697402) Ao, a main-belt asteroid
* .ao, top-level Internet domain code for Angola
* Adaptive optics, an astronomical imaging technology
* Ambient occlusion, a shading method in computer graphics
* AMSAT-OSCAR, a satellite naming convention
* Applied Optics, scientific journal published by the Optical Society of America (OSA)
* Arctic oscillation, a climate pattern
* Atomic orbital, in physics and chemistry
* Ao, the atomic symbol for the misidentified chemical element Ausenium.
* Acridine orange, a fluorescent dye
* Authorship obfuscation, a privacy technique

## Surnames and initials

* Ao (surname) (敖), a Chinese surname
* Ou (surname) (区/區 and 欧/歐), romanized as Ao in Cantonese
* Ao Omae (大前 粟生, Ōmae Ao, born 1992), Japanese fiction writer
* Aaron Owens (born 1976), American streetball player

## Other uses

* Alphabetically ordered
* Ao (color)
* Ao (digraph)
* Ao languages
* Ao Naga, an Indian ethnic group
* ao or außerordentlicher, meaning extraordinary professor (academic rank in Germany)
* Australian Open, an annual tennis tournament in Melbourne, Australia
* A$^o$, an abbreviation of "Anno", meaning "In the year" (as in Anno Domini)
* Te Ao Māori (literally "The Māori world"), Māori cultures and traditions