| Abbreviation | Definition |
|---|---|
| OFL | Off-season Football League |
| OFS | Ohio's Future Stars |
| OFS | Orange FoamShell |
| OFSAA | Ontario Federation of School Athletic Associations |
| OFSC | Ontario Federation of Snowmobile Clubs |
| OG | Own Goal |
| OGA | Online Gamers Association |
| OGA | Oregon Golf Association |
| OGA | Oregon Gymnastics Academy |
| OGC | Open Game Content |
| OGR | Oregon Golf Review |
| OGSA | Oceanside Girls Softball Association |
| OGSA | Odessa Girls Softball Association |
| OGT | Online Golf Tour |
| OGT | Operation Game Thief |
| OGX | Online Gamers Xtreme |
| OGZ | Online Gambling Zone |
| OH | Olympic Hopefuls |
| OHA | Old Hobartians Association football club |
| OHA | Ontario Hockey Association |