| O/E | (findings) on examination 
| Others |
| O/E | Observed-to-expected ratio
| Others |
| O/E | On Examination
| Others |
| O/E | Output Electronics
| Others |
| O/E | upon examination:
| Others |
| O/ET | Orbiter/External Tank
| Others |
| O/F | Office File
| Others |
| O/F | Only Freight
| Others |
| O/F | Oxidizer-to-Fuel Ratio
| Others |
| O/J | Override/Jettison
| Others |
| O/L | OverLoad
| Others |
| O/L-RC | OverLoad-Reverse Current
| Others |
| O/N | Order-Notify
| Others |
| O/o | Office of
| Others |
| O/O | On Orbit
| Others |
| O/PLAN | Open Plan
| Others |
| o/r | On Request
| Others |
| O/R | Outside Radius
| Others |
| O/R | Oxygen Relief
| Others |
| O/S | Operations and Support life cycle phase
| Others |
| O/S | Opposite Side
| Others |
| O/S | Out of Stock
| Others |
| O/S | Out Standing
| Others |
| O/S | OverSeas
| Others |
| O/T | Oil Tanker
| Others |
| o/t | Other Times
| Others |
| O/THAN | Other Than
| Others |
| O/V | OverVoltage
| Others |
| O/V-U/V | Over-Voltage/Under-Voltage
| Others |
| O/W | Oil-in-water
| Others |
| o/w | otherwise
| Others |
| O05 | Rogers Field Airport, Chester, Pennsylvania USA
| Others |
| O1 | Officer grade: Ensign or 2nd Lieutenant
| Others |
| O10 | Officer grade: Admiral or General
| Others |
| O11 | Officer Grade: Fleet Admiral Or General of the Army
| Others |
| O11 | STILWELL CHEROKEE NATION Airport, Stilwell, Oklahoma
| Others |
| O1C | A protein molecule. Formula: 2ALPHA-(3-HYDROXYPROPYL)-1ALPHA,25-DIHYDROXYVITAMIN D3
| Others |
| O2 | Object Oriented
| Others |
| O2 | Officer grade: Lieutenant Junior Grade or 1st Lieutenant
| Others |
| O2 | Optimistic Orators Toastmasters Club
| Others |
| O2 SAT | Oxygen SATurated hemoglobin
| Others |
| O22 | Columbia Municipal Airport, Columbia, California USA
| Others |
| O26 | Lone Pine Airport, Lone Pine, California USA
| Others |
| O2A | Order-to-Activation
| Others |
| O2B | Owner to Business
| Others |
| O2C | Order to Cash
| Others |
| O2C | Order to Customer
| Others |
| O2CM | Object Class and Contracts Support Model
| Others |
| O2CV | Ostfold 2cv Klubb
| Others |
| O2I | Object-Oriented Interface
| Others |