| Abbreviation | Definition |
|---|---|
| OPAL | Of People And Land |
| OPCW | Organization for Prohibition of Chemical Weapons |
| OPDEC | Orleans Parish Democratic Executive Committee (New Orleans, Louisiana) |
| OPI | Office of Police Integrity |
| OPJ | Other People's Jobs |
| OPLW | Onafhankelijke Partij Leefbare Wijk |
| OPM | Organisasi Papua Merdeka |
| OPMT | Organizational Politics Mapping Technique |
| OPN | Okinawa Peace Network |
| OPP | One Power Party |
| OPPR | Observatory on Political Parties and Representation |
| OPT | Occupied Palestinian Territories |
| OPW | Oregon PeaceWorks |
| OPY | Out & Proud Youth |
| ORA | Organización Revolucionaria Anarquista |
| OREP | Oldham Race Equality Partnership |
| OREP | Oregonians for Renewable Energy Progress |
| ORM | Oak Ridges Markham |
| ORPP | Office of the Registrar of Political Parties |
| ORW | Operation Rescue West |