| Abbreviation | Definition |
|---|---|
| NWR | National Workhour Report |
| NWRS | National Workhour Reporting System |
| NYD | Not Yet Delivered |
| NZ | New Zealand |
| OBMC | Origin Bulk Mail Center |
| OCR/CS | Optical Character Reader/Channel Sorter |
| ODIS | Origin Destination Information System |
| OEL | Optional Endorsement Line |
| OFC | Office |
| OFM | On-line File Maintenance |
| OH | Ohio |
| OIC | Officer In Charge |
| OLQ | On-Line Query |
| OM | Oman |
| OMAS | Official Mail Accounting System |
| OMSS | Organizational Management Staffing System |
| ON | ONtario |
| ON | Ontario (Canada) |
| OP | Optional Procedure Mailing System |
| OPF | Official Personnel Folder |