| Abbreviation | Definition |
|---|---|
| OMG | Oh My Gobstopper |
| OMIM | Online Mendelian Inheritance in Man |
| ONN | Onion News Network |
| OOO | OpenOffice.Org |
| OOSL | Object-Oriented Scripting Language |
| OPJ | Other people's junk |
| OREP | Online Resource Efficiency Platform |
| OSC | Our Sports Central |
| OSCV | One Stop CV |
| OSD | Obsessive Sneaker Disorder |
| OSHC | Over Sky Health Care |
| OTP-USA | Official Tea Party USA |
| OTRS | Open Technology Real System |
| OTTC | Over The Top Comedy |
| OUG | Olivares Unlimited Gold |
| OW | Official Website |
| OWC | Orgasm World Championship |
| OWDS | Oxford Website Design Solutions |
| PA | Pokkén Arena |
| PBF | Pro Buffy Fic |