| Abbreviation | Definition |
|---|---|
| APARS | Accounts Payable Accounting and Reporting System |
| APO | Army Post Office |
| APS | Adjustment Processing System |
| APT | Apartment |
| APWU | American Postal Workers Union |
| AQ | Antarctica |
| AR | Argentina |
| AR | Armenia |
| ARM | Accelerated Reply Mail |
| AS | Adult Signature |
| AS | American Samoa |
| ASC | Accounting Service Center |
| ASC | Adjusted Service Commitment |
| ASF | Administrative Support Facility |
| ASF | Auxiliary Service Facility |
| ASM | Administrative Support Manual |
| ASR | Adult Signature Required |
| AT | Austria |
| AU | Australia |
| AVE | Avenue |