| Acronym | Meaning |
| AAT | Australian Antarctic Territory |
| AAV | Amphibious Assault Vehicle |
| AAWC | Anti-Air Warfare Commander |
| AB | Able Seaman (rank) |
| AB | Abkhaz Language (ISO 639-1 Code) |
| ABA | American Bar Association - American Basketball Association - American Beverage Association - American Bicycle Association - American Birding Association - Australian Broadcasting Authority |
| ABB | ASEA Brown Boveri (Swiss-Swedish Multinational Company) |
| ABBA | Agnetha |
| ABC | Abstinence |
| ABCA | American Border Collie Association - American |
| ABCS | (U.S.) Army Battle Command System |
| ABET | Accreditation Board For Engineering And Technology |
| ABIN | Ag?ncia Brasileira De Intelig?ncia (Brazilian Intelligence Agency) |
| ABK | Abkhaz Language (ISO 639-2 Code) |
| ABL | American Basketball League |
| ABLE | AirBorne Law Enforcement (police Air Support Unit) |
| ABM | Anti-Ballistic Missile - Asynchronous Balanced Mode - Automated Banking Machine |
| ABMC | American Battle Monuments Commission |
| ABN | Australian Business Number (a Number Issued By The Australian Government As Registration Of A Business And Used For Taxation Purposes) |
| ABPI | Association Of The British Pharmaceutical Industry |
| ABRSM | Associated Board Of The Royal Schools Of Music |
| ABS | Acrylonitrile Butadiene Styrene - Anti-lock Braking System |
| ABSA | Amalgamated Banks Of South Africa (ab-sa) |
| ABSTRIPS | Abstraction-Based STRIPS |
| ABW | Aruba (ISO 3166 Trigram) |
| AC | Adriamycin-Cyclophosphamide (chemotherapy) - Air Conditioning - Alternating Current - Ante Christum (Latin |
| AC | Actinium |
| AC | Attocoulomb |
| ACA | Airspace Control Authority - Airspace Co-ordination Area - A Current Affair |
| ACARS | Aircraft Communication Reporting System |
| ACAS | Aboriginal Children's Advancement Society - Advisory |
| ACB | Asociaci›n De Clubs De Baloncesto (Spanish For Association Of Basketball Clubs) |
| ACC | U.S. Air Combat Command - Air Component Commander - Altocumulus Castellanus - Atlantic Coast Conference - Automatic Climate Control - Area Control Center |
| ACCA | Automatic Cloud Cover Assessment |
| ACCAC | Awdurdod Cymwysterau |
| ACCD | American Coalition Of Citizens With Disabilities |
| ACCS | Air Communications And Control Squadron |
| ACDA | Arms Control & Disarmament Agency |
| ACDC | Alternating Current Direct Current |
| ACE | Air Combat Emulator (computer Game) - Allied Command Europe - Armored Combat Earthmover - Automatic Computing Engine |
| ACES | Aerolineas Centrales De Colombia |
| ACF | American Car And Foundry - American Culinary Federation - Administration For Children And Families |
| ACHT | Average Call Hold Time |
| ACID | Atomicity |
| ACINT | Acoustic Intelligence |
| ACK | Acknowledge (telecommunications; Cf. NAK) |
| ACL | Access Control List - Anterior Cruciate Ligament |
| ACLOS | Automatic CLOS (missile Control System) |
| ACLS | Alternate Crops And Systems Lab |
| ACLU | American Civil Liberties Union |