| Acronym | Definition |
|---|
| AO | Angola |
| AO | And Others |
| AO | Anarchy-Online (PC MMORPG) |
| AO | Anarchy Online (internet game) |
| AO | Aosta (Val d'Aosta, Italy) |
| AO | Atlantic Ocean |
| AO | Account Of |
| AO | Adults Only |
| AO | Adults Only (ESRB game rating, 18 yrs. and up; graphic sex/violence) |
| AO | Abgabenordnung (German tax regulations) |
| AO | Among Others |
| AO | Other Articles (US postal service) |
| AO | Adaptive Optics |
| AO | Analog Output |
| AO | Order of Australia |
| AO | Advisory Opinion |
| AO | Applied Optics |
| AO | Announcement of Opportunity |
| AO | Age Old |
| AO | Arctic Oscillation |
| AO | Arctic Ocean |
| AO | Administrative Order |
| AO | Officer of the Order of Australia |
| AO | Area Office |
| AO | American Optical |
| AO | Atmosphere-Ocean |
| AO | Area of Operation(s) |
| AO | Audit Office |
| AO | Automated Office |
| AO | Abort Output (TELNET protocol) |
| AO | AntiOnline (computer security website) |
| AO | Argentum Online |
| AO | Anti-Oxidant |
| AO | Arbeitsgemeinschaft für Osteosynthesefragen (Association for the Study of Internal Fixation) |
| AO | Australian Airlines (IATA airline code) |
| AO | Acridine Orange |
| AO | Archives of Ontario |
| AO | Academy of Osseointegration |
| AO | Action Oriented |
| AO | Authorizing Official (for IMPAC Purchases) |
| AO | Atomic Oxygen |
| AO | Application Object |
| AO | Alexander Ovechkin (hockey player) |
| AO | Office of the Administrator |
| AO | Administration Officer |
| AO | Action Officer |
| AO | Autonomous Okrug |
| AO | Ambleside Online (homeschool curriculum) |
| AO | Atomic Orbital |
| AO | Advanced Organization (Church of Scientology) |
| AO | Appeals Office(r) |
| AO | Air Operation |
| AO | Adjustable Objective (rifle telescopic sight) |
| AO | Operational Availability |
| AO | Autres Objets (Canada universal postal union) |
| AO | Afrique Orientale (German East Africa) |
| AO | Accounts Office |
| AO | Account Owner |
| AO | Admit One |
| AO | Active Optical |
| AO | Air Officer |
| AO | Auslandsorganisation (foreign section of NSdAP) |
| AO | Answers Only (educational testing) |
| AO | Aircraft Operator |
| AO | Atlanto-Occipital (joint) |
| AO | Amphibious Operation |
| AO | Acousto Optics |
| AO | Aviation Officer |
| AO | Aerial Observer |
| AO | Atualidades Ornitológicas (Ivaiporã-PR, Brazil) |
| AO | Auxiliary Oiler (Ship Type) |
| AO | Aaron Owens (streetball player) |
| AO | Anglicans Online |
| AO | Air Observer |
| AO | Access Opening |
| AO | Associated Object |
| AO | Acquisition Objective |
| AO | Automated Operations |
| AO | Ambulance Officer (ambulance service; chiefly Australian) |
| AO | Atomic Operation |
| AO | Alpha et Omega (epigraphy) |
| AO | American Outfitters (store) |
| AO | Associate Office |
| AO | Athlitikos Omilos (Greek: Athletic Club) |
| AO | Abnormal Occurrence |
| AO | Annotated Outline |
| AO | Atelosteogenesis |
| AO | Assignment Officer |
| AO | Attendees Only |
| AO | Accommodation Officer |
| AO | Assembly Order |
| AO | Attack Objective |
| AO | Accredited Organization |
| AO | Auxiliary Operator (nuclear industry) |
| AO | Assisted Operations |
| AO | Access Ordering |
| AO | Anodal Opening |
| AO | Acronym Overload |
| AO | Automags Online |
| AO | Aortagram |
| AO | aviation ordnance person (US DoD) |
| AO | Apostolic Oblates |
| AO | Airdrome Officer |
| AO | Associate Post Office (also called associate office) |
| AO | Accompanying Object |
| AO | Administrative Office/ Officer |
| AO | Awards and Obligations |
| AO | Association Orukutuku |
| AO | Aeronautical Orders (orders authorizing a military person to perform duties in flight) |
| AO | Adaptive Onestep (IEEE) |
| AO | ACCS (Army Command and Control System) OSI (Operator System Interface) |
| AO | Aerosol Obscurant |
| AO | Arkansas and Ozarks Railway |
| AO | Air Overseas, Inc. |
| AO | Approximate Optimum Method |
| AO | (USN Rating) Aviation Ordnanceman |
| AO | Authorized Outage |