| Abbreviation | Definition |
|---|---|
| ARMA | Association for Renaissance Martial Arts |
| ARMS | Association for Renaissance and Medieval Swordsmanship |
| ARO | Alfa Romeo Owners |
| ARO | Aviation Recreational Organization |
| AROC | Alfa Romeo Owners Club |
| ARRL | American Radio Relay League |
| ARTPOP | Artistic Revolution Through The Potential Of Pop |
| ASA | After School Activity |
| ASAC | Aboyne Sub Aqua Club |
| ASCO | Association of Singer Car Owners Club |
| ASCWCC | Aperture Science Center Weighted Companion Cube |
| ASD | American Society of Dowsers |
| ASDS | Asociacion de Surfing Del Sur |
| ASFA | American Speeding Fines Association |
| ASITC | Advanced Snorkelling Instructor Training Course |
| ASK | Astrological Society of Kentucky |
| ASPEG | Anatolian Speleology Group Association |
| ASS | A Sensitive Senior |
| ASU | Aikido Schools of Ueshiba |
| ATA | American Trakehner Association |