| O | Engineering Order | - | Organizations |
| O&C | Operation And Checkout | - | Organizations |
| O&C | Operation(s) And Checkout (Building-was MSOB) | - | Organizations |
| O&C | Operations And Checkout | - | Organizations |
| O&C | Operations And Control | - | Organizations |
| O&FS | Operations And Flight Support | - | Organizations |
| O&M | Operation And Maintenance | - | Organizations |
| O&P | Operations And Procedures | - | Organizations |
| O&R | Overhaul And Repair | - | Organizations |
| O-NAV | Onboard Navigation | - | Organizations |
| O/B | Onboard | - | Organizations |
| O/B | Operational Base | - | Organizations |
| O/C | Operations Critical | - | Organizations |
| O/D | On Dock | - | Organizations |
| O/D | Outside Diameter | - | Organizations |
| O/ET | Orbiter/External Tank | - | Organizations |
| O/F | Oxidizet--to-Fuel Ratio | - | Organizations |
| O/L | Overload | - | Organizations |
| O/L-RC | Overload-Reverse Current | - | Organizations |
| O/R | Outside Radius | - | Organizations |
| O/R | Oxygen Relief | - | Organizations |
| O/V | Overvoltage | - | Organizations |
| O/V-U/V | Over Voltage/Under Voltage | - | Organizations |
| O2 | Oxygen | - | Organizations |
| OA | Office Of Applications (now OSTA) | - | Organizations |
| OA | Operational Aft (DSC Or MOM) | - | Organizations |
| OA | Operational Instrumentation MDM-Aft | - | Organizations |
| OA | Orbital Assembly | - | Organizations |
| OA | Output Axis | - | Organizations |
| OA | Overall | - | Organizations |
| OAA | Orbiter Access Arm | - | Organizations |
| OAA | Orbiter Access Arm | - | Organizations |
| OAA | Orbiter Alternate Airfield | - | Organizations |
| OAC | Quality Assurance Chart | - | Organizations |
| OAFD | Orbiter Air Flight Deck | - | Organizations |
| OAFTO | Orbiter Atmospheric Flight Test Office | - | Organizations |
| OAL | Overall Level | - | Organizations |
| OALC | Ogden Air Logistics Center | - | Organizations |
| OAMS | Orbital Attitude And Maneuvering System | - | Organizations |
| OAS | Office Automation System | - | Organizations |
| OAS | Orbiter Aeroflight Simulator | - | Organizations |
| OAS | Orbiter Atmospheric Simulator | - | Organizations |
| OAS | Orbiter Avionics System | - | Organizations |
| OASCB | Orbiter Avionics Software Control Board | - | Organizations |
| OASIS | Oceanic And Atmospheric Scientific Information System | - | Organizations |
| OASPL | Overall Sound Pressure Level | - | Organizations |
| OAST | Office Of Aeronautics And Space Technology | - | Organizations |
| OAT | Operational Acceptance Test | - | Organizations |
| OAT | Overall Test | - | Organizations |
| OB | Onboard | - | Organizations |
| OB | Operational Base | - | Organizations |
| OB | Outboard | - | Organizations |
| OBC | Onboard Computer | - | Organizations |
| OBCO | Onboard Checkout (Instrumentation) | - | Organizations |
| OBCS | Onboard Checkout Subsystem | - | Organizations |
| OBS | Observe | - | Organizations |
| OBS | Operational Bioinstrumentation System | - | Organizations |
| OBS | Operational Bioinstrumentation System | - | Organizations |
| OBS | Operational Biomed Sensors | - | Organizations |
| OBS | Operational Biomedical System | - | Organizations |
| OBV | Oxidizer Bleed Valve | - | Organizations |
| OC | On Center | - | Organizations |
| OC | On-Condition | - | Organizations |
| OC | Open Circuit | - | Organizations |
| OC | Orbital Check | - | Organizations |
| OC | Overcurrent | - | Organizations |
| OC | Quality Control | - | Organizations |
| OCALC | Oklahoma City Air Logistics Center | - | Organizations |
| OCC | Office Of Contract Compliance | - | Organizations |
| OCC | Operations Control Center | - | Organizations |
| OCD | Operational Capability Development | - | Organizations |
| OCDR | Orbiter Critical Design Review | - | Organizations |
| OCDU | Optics Coupling Data Unit (G&N) | - | Organizations |
| OCE | Ocean Color Experiment | - | Organizations |
| OCF | Onboard Computational Facility | - | Organizations |
| OCF | Orbiter Computational Facilities | - | Organizations |
| OCH | Orbiter Common Hardware | - | Organizations |
| OCM | Organic Content Monitor | - | Organizations |
| OCN | Order Control Number | - | Organizations |
| OCO | OMS Cutoff | - | Organizations |
| OCO | Open-Close-Open | - | Organizations |
| OCP | Output Control Pulse | - | Organizations |
| OCR | Optical Character Recognition | - | Organizations |
| OCRM | Orbiter Crash And Rescue Manuals | - | Organizations |
| OCS | Onboard Checkout System | - | Organizations |
| OCT | Octal | - | Organizations |
| OD | Operational Downlink/Downlist | - | Organizations |
| OD | Operations Directive | - | Organizations |
| OD | Outside Diameter | - | Organizations |
| OD | Oxygen Drain | - | Organizations |
| ODB | Operational Data Book | - | Organizations |
| ODC | Other Direct Costs | - | Organizations |
| ODCDR | Orbiter Delta CDR | - | Organizations |
| ODDS | Operational Data Delivery Services | - | Organizations |
| ODES | Optical Discrimination Evaluation Study | - | Organizations |
| ODF | Orbit Determination Facility | - | Organizations |
| ODIN | Orbital Design Integration (System) | - | Organizations |
| ODP | Operational Display Procedure | - | Organizations |
| ODR | OutPut Data Redundancy | - | Organizations |
| ODRAN | Operational Drawing Revision Advance Notice | - | Organizations |
