| Abbreviation | Definition |
|---|---|
| ORO | Oak Ridge Operations (United States Department of Energy) |
| ORO | Oak Ridge Operations, U. S. Department of Energy |
| ORO | Office of Research Oversight |
| ORR | Office of Refugee Resettlement |
| ORT | Oak Ridge Tennessee |
| ORT | Oak Ridge, Tennessee |
| ORT | Operational Resilience Team |
| ORW | Olentangy River Wetland Research Park |
| OS | Other Supplementary |
| OSA | Official Secrets Act |
| OSAC | Overseas Security Advisory Council |
| OSB | Ocean Studies Board |
| OSBA | Office of Small Business Advocate |
| OSBP | Office of Small Business Programs |
| OSC | Office of Special Counsel |
| OSCA | Open Space Conservation Area |
| OSCAR | OSHA on-Site Consultation Achievement Recognition |
| OSCE | Office of Child Support Enforcement |
| OSCE | Organization for Security and Co-operation in Europe |
| OSDBU | Office of Small and Disadvantaged Business Utilization |