| AA | Accounting Authority |
| AAIC | Accounting Authority Identification Code |
| AAL | ATM Adaptation |
| AA/TDMA | Adaptive Assignment TDMA |
| ABE | Alternative Billing Entity |
| ABM | Apogee Boost Motor |
| ABM | Asynchronous Balanced Mode |
| ABR | Audio Broadcast Receiver |
| ABR | Available Bit Rate |
| ABU | Asian Broadcasting Union |
| AC | Alternating Current |
| AC | Assignment Channel |
| ACAST | Advisory Committee on the Application of Science and Technology to Development |
| ACC | Antenna Control Console |
| ACC | Automatic Chroma Correction |
| ACD | Automatic Call Distribution |
| ACE | Audio Connecting Equipment |
| ACI | Adjacent Channel Interference |
| ACK | Acknowledgement |
| ACME | Analogue Circuit Multiplication Equipment |
| ACP | Adjacent Channel Power |
| ACPR | Adjacent Channel Power Ratio |
| ACPR | Adjacent Channel Protection Ratio |
| ACPW | Asymmetrical Coplanar Waveguide |
| ACS | Access Control System |
| ACS | Attitude Control Subsystem |
| ACTP | Abridged Condensed Time Plan |
| ACTS | Advanced Communication Technology Satellite |
| ACU | Antenna Control Unit |
| A/D | Analogue to Digital |
| ADACS | Attitude Determination and Control System |
| ADC | Analogue to Digital Conversion |
| ADCE | Attitude Determination and Control Electronics |
| ADCS | Attitude Determination and Control Subsystem |
| ADDT | Advanced Digital Television Technologies |
| ADE | Above Deck Equipment |
| ADM | Adaptive Delta Modulation |
| ADN | Advanced Digital Network |
| ADPCM | Adaptive Differential Pulse Code Modulation |
| ADR | Astra Digital Radio |
| ADSL | Asynchronous Digital Subscriber Line |
| ADX | Astra 1D eXtender |
| AES | Aircraft Earth Station |
| AF | Audio Frequency |
| AFC | Automatic Frequency Control |
| AFETR | Air Force Eastern Test Ranges |
| AGC | Automatic Gain Control |
| A-H | Ampere Hour |
| A-H | Amp-House |
| AIAA | American Institute of Aeronautics and Astronautics |
| AIS | Alarm Indication Signal |
| AKM | Apogee Kick Motor |
| ALT | Altitude |
| AM | Amplitude Modulation |
| AM | Apogee Motor |
| A-MAC | Type A Multiplexed Analogue Components |
| AMF | Apogee Motor Firing |
| AMPS | Advanced Mobile Phone System |
| AMS | Attitude Measurements Sensor |
| AMSS | Aeronautical Mobile Satellite Service |
| ANC | Automatic Nutation Control |
| ANSI | American National Standards Institute |
| ANTEL | Administation Nacional de Telecomunicaciones |
| AOCS | Attitude and Orbit Control System |
| AoD | Audio on Demand |
| AOR | Atlantic Ocean Region |
| AOTS | Advanced Orbital Test Satellite |
| APC | Adaptive Predictive Coding |
| APC | Autonomous Payload Controller |
| APCS | Autonomous Payload Control System |
| APD | Avalanche Photodiode Detector |
| APE | Antenna Positioning Electronics |
| APE | Attitude Processor Electronics |
| APM | Amplitude Phase Modulation |
| APM | Antenna Positioning Mechanism |
| APS | Auxilliary Power Supply |
| APSK | Amplitude Phase Shift Keying |
| AR | Axial Ratio |
| ARA | Angular Rate Assembly |
| ARC | Administrative Radio Conference |
| ARF | Alternate Recovery Facility |
| ARINC | Aeronautical Radio Inc |
| ARP | Address Resolution Protocol |
| ARPA | Advanced Research Projects Agency |
| ARQ | Automatic Repeat reQuest |
| ARTI | Arab Regional Telecommunications Institute |
| ASA | American Standards Association |
| ASBU | Arab States Broadcasting Union |
| ASCII | American Standard Code for Information Exchange |
| ASCO | Arab Satellite Communications Organisation |
| ASEAN | Association of South East Asian Nations |
| ASIC | Application Specific Integrated Circuit |
| ASK | Amplitude Shift Keying |
| ASPR | Automatic Satellite Position Report |
| ASR | Automatic Send and Receive |
| ASS | Amateur Satellite Service |
| ASSR | Acquisition and Steady State Reception Procedure |
| ASU | Acquisition and Synchronisation Unit |
| AT | Acceptance Test |
| ATB | All Trucks Busy |
| ATC | Adaptive Transform Coding |
| ATDA | Augmented Target Docking Adaptor |
| ATDE | Adaptive Time Domain Equaliser |
| ATIS | Automatic Transmitter Identification System |
| ATM | Asynchronous Transfer Mode |
| ATM | Automatic Teller Machine |
| ATME | Automatic Transmission Measuring Equipment |
| ATP | Acceptance Test Procedure |
| ATU | Arab Telecommunications Union |
| AU | Astronomical Unit |
| AUC | Authentication Centre |
| A/V | Audio Visual |
| AVD | Alternate Voice/Data |
| AWG | American Wire Gague |
| AWGN | Additive White Gaussian Noise |
| AZ | Azimuth |
