| A/D | Analog-to-Digital |
| AA | Adaptive Array |
| AAA | Authentication, Authorization, and Accounting |
| AAL-[x] | ATM Adaptation [layer x] |
| AAS | Adaptive Antenna Systems |
| ABC | Activity-Based Costing |
| ABR | Available Bit Rate |
| ABS | Automatic Brake System |
| AC | Alternating Current |
| A-C | Antenna Carrier |
| ACC | Adaptive Cruise Control |
| ACD | Automatic Call Distributor |
| ACH | Automated Clearinghouse |
| ACK | Acknowledgement |
| ACL | Access Control List |
| ACLEP | Adaptive Code Excited Linear Prediction |
| ACLR | Adjacent Channel Leakage Ratio |
| ACM | Address Complete Message |
| ACP | Adjacent Channel Power |
| ACPR | Adjacent-Channel Power Ratio |
| ACR | Alternate Carrier Routing |
| ACR | Anonymous Call Rejection |
| ACS | Adjacent Channel Sensitivity |
| ACTS | Advanced Communications Technology Satellite |
| ADAS | Advanced Driver Assistance System |
| ADC | Analog-to-Digital Converter |
| ADM | Add/Drop Multiplexer |
| ADPCM | Adaptive Differential Pulse Code Modulation |
| ADS | Add/Drop Switch |
| ADS | Advanced Design System |
| ADSI | Analog Display Services Interface |
| ADSL | Asymmetrical Digital Subscriber Line |
| AET | Advanced Energy Technology |
| AFA | Adaptive Frequency Agile |
| AFE | Analog Front End |
| AFF | Analog Front-Forward |
| AGC | Automatic Gain Control |
| AGW | Agent Gateway |
| AIM | Advanced Intelligent Messaging |
| AIN | Advanced Intelligent Network |
| AIS | Automatic Identifiction System |
| AISG | Antenna Interface Standards Group |
| ALD | Antenna Line Devices |
| ALI | Automatic Location Identification |
| ALU | Arithmetic Logic Unit |
| AM | Amplitude Modulation |
| AMA | Automatic Messaging Account |
| AMC | Advanced Modulation and Coding |
| AMI | Alternate Mark Inversion |
| AMI-C | Automotive Multimedia Industry Consortium |
| AMPS | Advanced Mobile Phone System |
| AN | Access Network |
| ANI | Automatic Number Identification |
| ANM | Answer Message |
| ANSI | American National Standards Inst. |
| ANX | Automotive Network Exchange |
| AODV | Ad-Hoc on Demand Distance Vector |
| AOL | America Online |
| AON | All-Optical Network |
| AP | Access Point |
| AP | Access Provider |
| APC | Automatic Power Control |
| APCO | Association of Public-Safety Communications Officials-International |
| API | Application Programmer’s Interface |
| APIs | Application Programer's Interface |
| APON | ATM Passive Optical Network |
| APS | Antenna Positioning System |
| ARB | Arbitrary Wavefrom Generator |
| ARCNET | Attached Resource Computer Network |
| ARI | Assist Request Instruction |
| ARIB | Association of Radio Industries and Businesses |
| ARM | Asynchronous Response Mode |
| ARMS | Authentication, Rating, Mediation, and Settlement |
| ARP | Address Resolution Protocol |
| ARPANET | Advanced Research Projects Agency Network |
| ARPU | Average Revenue Per Customer |
| ARQ | Automatice Repeat Request |
| A-Rx | Analog Receiver |
| AS | Autonomous System |
| AS | Application Server |
| ASAM | ATM Subscriber Access Multiplexer |
| ASC | Accredited Standards Committee |
| ASCII | American Standard Code for Information Interchange |
| ASE | Amplified Spontaneous Emission |
| ASIC | Application-Specific Integrated Circuit |
| ASIP | Application-Specific Instruction Processor |
| ASK | Amplifier Shift Keying |
| ASM | Antenna Switch Module |
| ASON | Automatically Switched Optical Network |
| ASP | Application Service Provider |
| ASR | Access Service Request |
| ASR | Answer-Seizure Rate |
| ASR | Automatic Service Request |
| ASR | Automatic Speech Recognition |
| ASSP | Application-Specific Standard Part |
| ASTN | Automatically Switched Transport Network |
| ASTN | Analog Switched Telephone Network |
| ATC | Automatic Temperature Control |
| ATE | Automated Test Equipment |
| ATIS | Alliance for Telecommunications Industry Solutions |
| ATM | Asynchronous Transfer Mode |
| ATM | Automated Teller Machine |
| ATMF | ATM Forum |
| ATP | Analog Twisted Pair |
| ATU-C | ADSL Transmission Unit-CO |
| ATU-R | ADSL Transmission Unit-Remote |
| A-Tx | Analog Transceiver |
| AUI | Attachment Unit Interface |
| AVERT | Automated Vulnerability Evaluation for Risk of Terrorism |
| AVI | Audio Video Interleaved |
| AWG | Arrayed Waveguide Grating |
| AWGN | Additive White Gaussian Noise |
| AYUTOS | As-Yet-Un-Thought-Of Services |