| | oasrn | | On a site right now |
| | oatus | | On A Totally Unrelated Subject |
| | oaus | | On A Unrelated Subject |
| | oaus | | On An Unrelated Subject |
| | OBE | | Order of the British Empire |
| | OBEX | | object exchange |
| | OBICU | | Obstetric Intensive Care Unit |
| | OBKB | | Okay bye bye |
| | OBKB | | Okay, bye bye |
| | OBO | | Or Best Offer |
| | OBTWIAU | | oh by the way I adore you |
| | OC | | Operations Centre |
| | OCD | | Obsessive compulsive disorder |
| | OCIA | | of course i am |
| | OCONUS | | Outside Continental United States |
| | OCONUS | | Outside continetal United states |
| | OCR | | official cash rate |
| | OCR | | Optical Character Recognition |
| | OD | | oh dear |
| | OD | | overdose |
| | OD | | Overdraft |
| | ODBC | | Open DataBase Connectivity |
| | ODI | | One Day International |
| | ODL | | Oh Dear Lord |
| | ODMA | | Open Document Management API |
| | ODPM | | Office Of the Deputy Prime Minister |
| | OE | | Original Equipment |
| | OE | | Overseas Experience |
| | OECD | | Organisation for Economic Co-operation and Development |
| | OED | | Oxford English Dictionary |
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