| O | Overcooked 
| Others |
| O | Overdistance
| Others |
| O | Overhaul
| Others |
| O | Overlay
| Others |
| O | Overs
| Others |
| O | Overt
| Others |
| O | Owen
| Others |
| O | Owner
| Others |
| O | Ownership
| Others |
| O | Oxygen
| Element |
| o | pint
| Others |
| O | Pyrrolysine
| Others |
| O | UNIX Object file
| Others |
| O!RUL8,2? | Oh! Are You Late, Too?
| Others |
| O# | Overton Number
| Others |
| O$$ | Outfile (Sprint)
| Others |
| O&A | Odontectomy and Alveolectomy
| Others |
| O&C | Official and Confidential
| Others |
| O&C | Oldham and Crowther
| Others |
| O&C | Operation and Checkout
| Others |
| O&C | Operations and Control
| Others |
| O&D | Origin and Destination
| Others |
| O&DCVC | Oban and District Classic Vehicle Club
| Others |
| O&E | Observation and Examination
| Others |
| O&FS | Operations and Flight Support
| Others |
| O&G | Obstetrics and Gynaecology
| Others |
| O&G | Oil and Gas
| Others |
| O&G | Oil and Grease
| Others |
| O&I | Operations and Intelligence
| Others |
| O&IA | Operations and Integration Agreement
| Others |
| O&M | Operation and Maintenance
| Others |
| O&M | Operations & Maintenance
| Others |
| O&M | Operations and Maintenance
| Others |
| O&M | Organization and Management
| Others |
| O&M | Organization and Method
| Others |
| O&MC | Operation and Maintenance Cost
| Others |
| O&O | Offshoring And Outsourcing
| Others |
| O&O | Operational and Organizational
| Others |
| O&O | Organizations and Operations
| Others |
| O&O | Over and Out
| Others |
| O&O | Owned & Operated
| Others |
| O&O | Owned and Operated
| Others |
| O&OP | Operational and Organizational Plan
| Others |
| O&P | Operating and Planning
| Others |
| O&P | Operations and Procedures
| Others |
| O&P | Ova and Parasite
| Others |
| O&P | Ova and Parasites
| Others |
| O&R | Overhaul and Repair
| Others |
| O&S | Operations and Support
| Others |
| O&V | Opel and Vauxhall
| Others |