| Abbreviation | Definition |
|---|---|
| OBA | Ontario Basketball Association |
| OBE | Order Of British Empire |
| OBF | Ohio Bicycle Federation |
| OBL | Official Big League |
| OBN | Ohio Balloon Network |
| OBO | Original Bets Only |
| OBP | On Base Percentage |
| OBP | One BIG Punch |
| OBR | Official Baseball Rules |
| OBRA | Oregon Bicycle Racing Association |
| OBT | Off the Beaten Track |
| OBX | Oshawa Sports Centre |
| OC | Offensive Crouching |
| OC | Open Canoe |
| OC | Open Cup |
| OC | Original club |
| OCA | Olympic Council of Asia |
| OCBC | Orange County Badminton Club |
| OCC | One City Challenge |
| OCET | Oberlin College Equestrian Team |