| Abbreviation | Definition |
|---|---|
| ORAT | Off Road All Terrain |
| ORC | Organic Rankine Cycle |
| ORD | Chicago O'Hare International Airport |
| ORD | Operational Readiness Date |
| ORD | Operational Readiness Demonstration |
| ORFS | Origin Rail Freight |
| ORSAR | Ontario Road Safety Annual Report |
| ORTP | Oahu Regional Transportation Plan |
| ORV | Off Road Vehicle |
| ORV | Off Road Vehicles |
| OS | Optional Stopping |
| OS&D | Over, Short, and Damaged |
| OSCA | Officina Specializzata Costruzione Automobili |
| OSD | Out of System Damages |
| OSD | Out of System & Damages |
| OSDA | Oceanic System Development and Support |
| OSF | Off-Side Front |
| OSIM | Ontario Structure Inspection Manual (Canada) |
| OSR | Old Spanish Road |
| OSR | Old Stage Route |