| Abbreviation | Definition |
|---|---|
| ACCUM | Accumulator |
| ACE | ASCII Compatible Encoding |
| ACEN | Assembly of Captive European Nations |
| ACP | ANSI Code Page |
| ACQT | Advance Clock to Quitting Time |
| ACR | Advanced Code Reconstruction |
| ACR | Alternate Conditional Request |
| ACR | Assembly Concurrent Resolution |
| ACS | Active Character Select |
| ACS | Alternate Character Set |
| ADC | Add with Carry |
| ADD | Addition |
| ADF | Automatically Defined Function |
| ADIW | Add Immediate Word |
| ADIW | Word-wide Addition |
| AF | Address Family |
| AF | Advanced Functions |
| AFF | Add Fudge Factor |
| AFHB | Align Fullword on Halfword Boundary |
| AFI | Application Field Identifier |