| Abbreviation | Definition |
|---|---|
| OP | Opening Pressure |
| OPAL | Open Physics Abstraction Layer |
| OPALS | Optronic, Photonic, and Advanced Laser Simulator |
| OPC | Optical Particle Counter |
| OPCB | Optical Printed Circuit Board |
| OPCPA | Optical Parametric Chirped Pulse Amplification |
| OPD | Ocean Physics Department |
| OPD | Optical Path Difference |
| OPEB | Ordinary Potential Energy Box |
| OPERA | Oscillation Project with Emulsion tRacking Apparatus |
| OPLL | Optical Phase Locked Loop |
| OPMAS | Optical Pumping and Magic Angle Spinning |
| OPO | Optical Parametric Oscillator |
| OPS | Optical Physical Section |
| OPSL | Optically Pumped Semiconductor Laser |
| OPSn | Optical Physical Section n |
| OPSO | Optimized Particle Swarm Optimization |
| ORP | Optimization of Radiation Protection |
| ORT | Oak Ridge Tennessee |
| OSC | Organic Solar Cell |