| Abbreviation | Definition |
|---|---|
| OMACC | Ohio Micromachined Analytical Chemistry Consortium |
| OMP | Orotate MonoPhosphate |
| OMZ | Oxygen Minimum Zone |
| ON | Oxidation Number |
| OND | Organic Nitrogen Detection |
| OO | Orbitally Ordered |
| OP | Organo-Phosphate |
| OP | Osmotic Pressure |
| OP | Oxidative Phosphorylation |
| OPCW | Or The Prohibition Of Chemical Weapons |
| OPCW | Or The Prohibiton Of Chemical Weapons |
| OPCW | Organisation for Prohibition of Chemical Weapons |
| OPCW | Organisation for the Prohibition of Chemical Weapons |
| OPM | One Piece Magnesium |
| OPT | OPTical grade solvent |
| OQS | Occupied Quantum State |
| ORP | Oxidation Reduction Potential |
| ORR | Oxidation- Reduction Reaction |
| ORR | Oxidation-Reduction Reaction |
| ORTEP | Oak Ridge Thermal Ellipsoid Plot |