| Abbreviation | Definition |
|---|---|
| ORHS | Orrville Railroad Heritage Society |
| ORS | Operational Research Society |
| ORSI | Associazione Italiana di Ricerca Operativa |
| ORSI | Operations Research Society of Italy |
| ORSJ | ??????????·?????? |
| ORSJ | Nihon Opereeshiyonsu Risaachi Gakkai |
| ORSJ | Operations Research Society of Japan |
| ORSS | Operational Research Society of Singapore |
| ORSSA | Operasionele Navorsingsvereniging van Suid-Afrika |
| ORSSA | Operations Research Society of South Africa |
| OS | Oceanography Society |
| OSA | Ontario Society of Artists |
| OSA | Open Society Archives |
| OSA | Optical Society A |
| OSA | Optical Society of America |
| OSA | Orissa Society of America |
| OSA | Orissa Society of Americas |
| OSAE | Oklahoma Society of Association Executives |
| OSAF | Ohio Society of American Foresters |
| OSAF | Oregon Society of American Foresters |