| Abbreviation | Definition |
|---|---|
| OPA | Open Platform for Architecture |
| OPA | Optimal Performance Architecture |
| OPB | One-Piece Building |
| OPBS | One-Piece Building Specifcation |
| OPC | Ordinary Portland Cement |
| OPMA | Open Platform Management Architecture |
| OPSD | Ontario Provincial Standard Drawing |
| OPSO | OverPressure ShutOff |
| OPSS | Ontario Provincial Standard Specification |
| OPSV | OverPressure Safety Valve |
| OPV | Over-Pressure Valve |
| OS | Open Space |
| OSA | Office of the State Architect |
| OSA | Open Simulation Architecture |
| OSA | Open Systems Architecture |
| OSOA | Open Service Oriented Architecture |
| OSR | Open Side Ruled |
| OT | Overflow Threshold |
| OTS | Open To Sky |
| OUA | Office of University Architects |