| Abbreviation | Definition |
|---|---|
| ONV | Österreichischer NaturistenVerband |
| OOH | Dave Dravecky's Outreach Of Hope |
| OOR | Off Our Rockers |
| OPADD | Ontario Partnership on Aging Developmental Disabilities |
| OPADD | Ontario Partnership on Aging & Developmental Disabilities |
| OPAL | One People of Australia League |
| OPAL | Overseas Pharmaceutical Aid for Life |
| OPAMS | Outreach Planning And Mobile Sources |
| OPB | Oregon Public Broadcasting |
| OPEN | Orphan Pets Enjoy Nature |
| OPF | Oregon Psychoanalytic Foundation |
| OPG | Online Policy Group |
| OPH | Operation Phone Home |
| OPIRG | Ontario Public Interest Research Group |
| OPIRG-GRIPO | Ontario Public Interest Research Group-le Groupe de Recherche d'Intérêt Public de l'Ontario |
| OPJ | Our Pride & Joy |
| OPKN | Our Place Kings Norton |
| OPN | Our People Network |
| OPRA | Organization Public Relationship Assessment |
| OPRA | Ottawa Photonics Research Alliance |