| Abbreviation | Definition |
|---|---|
| ORCA | Ontario Residential Care Association |
| ORCA | The Online Racing Championship Association |
| OREA | Ontario Real Estate Association |
| OREA | Oregon Retired Educators Association |
| ORHA | Ontario Residence Hall Association |
| ORR | Office of Rail Regulation |
| ORRA | Orlando Regional Realtor Associations |
| ORRA | Orraoff Road Radio Association |
| ORRA | Otago Rugby Referees Association |
| ORS | Orthopaedic Research Society |
| ORTA | Ohio Retired Teachers Association |
| OSCA | Officine Specializate Costruzione Automobili |
| OSCA | Ohio State Coroners' Association |
| OSCA | On-Site Communications Association |
| OSCC | Ontario Society of Clinical Chemists |
| OSD | Office of Supplier Diversity |
| OSGA | Off Shore Gaming Association |
| OSGA | Oregon Sheep Growers Association |
| OSIP | Organization of Spirit Industry Providers |
| OSM | Office of Strategy Managment |