| Abbreviation | Definition |
|---|---|
| NZB | Non-Zero Binary |
| O | Omega |
| O | Omicron |
| O | Oort |
| O | Out |
| O&C | Operation and Checkout |
| O&C | Operations and Control |
| O&FS | Operations and Flight Support |
| O&IA | Operations and Integration Agreement |
| O&M | Operations and Maintenance |
| O&P | Operations and Procedures |
| O&R | Overhaul and Repair |
| O/B | Onboard |
| O/B | Operational Base |
| O/C | Operations Critical |
| O/D | On Dock |
| O/D | Outside Diameter |
| O/E | Output Electronics |
| O/ET | Orbiter/External Tank |
| O/F | Oxidizer-to-Fuel Ratio |