| | ACLU | | American Civil Liberties Union |
| | ACMS | | Advanced Content Management System |
| | ACNA | | Access Carrier Name Abbreviation |
| | ACRONYM | | abbreviated coded rendition of name yielding meaning |
| | ACRONYM | | an abbreviation formed from the initial letters of words |
| | AD&D | | Accidental Death & Dismemberment |
| | AD&D | | Advanced Dungeons and Dragons |
| | ADAD | | Another Day Another Dollar |
| | ADBB | | all done bye bye |
| | ADBB | | all done, bye, bye |
| | ADC | | automated data collection |
| | ADCOMSUBORDCOMPHIBSPAC | | Administrative Command, Amphibious Forces, Pacific Fleet Subordinate Command |
| | ADCP | | Air Defense Communications Platform |
| | ADHD | | attention deficit hyperactive disorder |
| | adidas | | all day i dream about sex |
| | adidas | | all day i dream about sex. |
| | ADIH | | another day in hell |
| | ado | | active data objects |
| | ado | | adolescent |
| | ADODB | | Active Data Objects DataBase |
| | ADPCM | | Adaptive Differential Pulse Code Modulation |
| | ADRD | | Alzheimer's Disease or a Related Disorder |
| | ADSI | | Active Directory Service Interfaces |
| | ADSL | | Asymmetric Digital Subscriber Line |
| | ADSR | | Attack, Decay, Sustain, Release |
| | AEAP | | as early as possible |
| | aelf | | Artificially Engineered Life Form |
| | aelfs | | Artificially Engineered Life Forms |
| | aes | | Advanced Encryption Standard |
| | AEST | | Australian Eastern Standard Time |
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