| Abbreviation | Definition |
|---|---|
| OSCA | Ovenden Sports and Community Arena |
| OSDA | Old School Derby Association |
| OSFC | Ohio Select Futbol Club |
| OSFM | Operation Sports Full Minors |
| OSGA | Ontario Senior Games Association |
| OSGCC | Owen Sound Golf and Country Club |
| OSMI | Optima Sports Management International |
| OSMI | Orthopaedics and Sports Medicine Institute |
| OSRS | Ohio Spring Race Series |
| OSS | Ontario Sire Stakes |
| OSSD | Open Source Sports Directory |
| OSSR | Olympic Sports and Spine Rehabilitation |
| OST | Orcish Stone Thrower |
| OSW | Official Scrabble Words |
| OSW | Old School Wrestling |
| OSZ | Ottawa Ski Zone |
| OSZ | Outaouais Ski Zone |
| OT | Old Trafford |
| OT | One Thrown |
| OT | Outdoor Track |