| Abbreviation | Definition |
|---|---|
| ORL | ORLando Magic |
| ORM | One Rep Max |
| ORN | Obligatory Running Note |
| ORP | Our Rare Pairings |
| ORPC | Oundle Rifle and Pistol Club |
| ORQ | Ocean Racing Queensland Class Association, Inc. |
| ORSA | Oak Ridge Sportsmen's Association |
| ORSA | Ohio Recreational Sports Association |
| ORT | Oak Ridges Trail (Ontario, Canada) |
| ORU | Ontario Rugby Union |
| ORX | On-line Racing eXtreme |
| OS | Optimal Strategy |
| OS | Outside Shot |
| OSA | Omaha Sports Academy |
| OSA | Ontario Soccer Association |
| OSA | Outdoor Soccer Of America |
| OSB | Opposition Stolen Bases |
| OSC | Ottawa Ski Club |
| OSCA | Organisation for Sports Club Administration, Ltd. |
| OSCA | Osteopathic Sports Care Association |