| Acronym | Definition |
|---|
| AAO | Archives Association of Ontario |
| AAO | America's Army Operations (game) |
| AAO | Amino Acid Oxidase |
| AAO | Am Angegebenen Ort (German) |
| aaO | am angegebenen Ort |
| AAO | Approved Acquisition Objective |
| AAO | Anodic Alumina Oxide |
| AAO | Association of Aviation Ordnancemen |
| AAO | Army Acquisition Objective |
| AAO | Authorized Acquisition Objective |
| AAO | Administrative Appeal Office (U.S. Citizenship and Immigration Services) |
| AAO | Association des Amis des Oiseaux (French) |
| AAO | Awake, Alert and Oriented (medical) |
| AAO | Association des Archives de l'Ontario (French: Archives Association of Ontario) |
| AAO | Acetaldehyde Oxime |
| AAO | Airborne Area of Operation |
| AAO | Audio, Acoustique et Ondes (French: Audio, Acoustics and Waves) |
| AAO | Area Audit Office |
| AAO | Autonomous Aircraft Operations |
| AAO | Adverse Assumption Obstacle |
| AAO | American's Army: Operations (game) |
| AAO | Army Acquisition Organization |
| AAO | America's Army: Operations (game) |
| AAO | Alert and Oriented |
| AAO | Alumni Affairs Office (various schools) |
| AAO | Anglo-Australian Observatory |
| AAO | Against All Odds |
| AAO | American Academy of Ophthalmology |
| AAO | American Academy of Optometry |
| AAO | American Academy of Osteopathy |
| AAO | American Association of Orthodontists |
| AAO | Age At Onset |
| AAO | Against All Odds (gaming clan) |
| AAO | Alpha and Omega |
| AAO | Academic Affairs Office (various schools) |
| AAO | American Academy of Otolaryngology (Head & Neck Surgery) |