| Abbreviation | Definition |
|---|---|
| O/F | Oxidizet-to-Fuel Ratio |
| O/L | Overload |
| O/L-RC | Overload-Reverse Current |
| O/O | On Orbit |
| O/R | Outside Radius |
| O/R | Oxygen Relief |
| O/V | Overvoltage |
| O/V-U/V | Over Voltage/Under Voltage |
| O/V-U/V | Over-Voltage/Under-Voltage |
| O2 | Oxygen |
| OA | Office of Applications (now OSTA) |
| OA | Operational Aft (DSC or MOM) |
| OA | Operational instrumentation MDM (Manipulator Deployment Mechanism) -Aft |
| OA | Operational Instrumentation MDM-Aft |
| OA | Operations Agreement |
| OA | Orbital Assembly |
| OA | Output Axis |
| OAA | Orbiter Access Arm |
| OAA | Orbiter Alternate Airfield |
| OAET | Office of Aeronautics, Exploration, and Technology |