| Abbreviation | Definition |
|---|---|
| OAU | Organization of African Unity |
| OAUS | Occupy Africa Unity Square |
| OAY | Organisation of African Youth |
| OAY | Organization of African Youth |
| OB | Ossewa Brandwag |
| OEAS | Organization of Emerging African States |
| OEOA | Office of Emergency Operations in Africa (UN) |
| OFA | Our Family in Africa |
| OFWA | Open Foundation West Africa |
| OHASA | Oral Hygienists Association of South Africa |
| OHASA | Oral Hygienists' Association of South Africa |
| OMG! | Oh My God! |
| OMLACSA | Old Mutual Life Assurance Company South Africa |
| OMVS | Organisation pour la Mise en Valeur du Fleuve Senegal |
| OOA | Out of Africa |
| OPC | Ovamboland People's Congress |
| OPCV | Office of Public Counsel for Victims (Kenya) |
| OPM | Offices Professional Missionaries |
| OPO | Ovamboland People's Organization |
| OPSA | Office Professionals of South Africa |