- AA (Administrative Assistant)
- Access Control
- Acknowledgement
- Action Plan
- Active program
- Active Window
- Added Value
- Administrivia
- Advanced Interactive Executive (AIX)
- Advanced Peer-to-Peer Networking
- Agent
- Aggregate
- Aggressive
- Alarm
- Alert
- Alias
- All Blue
- All hands meeting
- All points addressable
- Allocate
- American National Standards Institute (ANSI)
- Analog
- Ancillary equipment
- Announce
- Append
- Appendage
- Applet
- Application
- Application desktop toolbar
- Application Program
- Application Program Interface
- Architect
- Archive
- Ariticial Intelligence
- ASCII (American national Standard Code for Information Interchange)
- Asymmetric
- Asynchronous
- Asynchronous Communication
- Asynchronous Transfer Mode (ATM)
- Attribute
- Authentication
- Authorization
- Authorized program analysis report (APAR)
- AUTOEXEC.BAT file
- Automatic Calling Unit (ACU)
- Automatic Logoff
- Automatic Logon
- Auxiliary equipment
- Back Burner
- Back Level
- Backbone
- Backbone network
- Background Picture
- Background Process
- Background Task
- Ballpark
- Bandwidth
- Basic Input/Output System
- Batch
- Batch File
- Baud
- Bean
- Bells and Whistles
- Belly Up
- Best-Of-Breed
- Beta Test
- Big Iron
- Bit
- Bitmap
- Block
- Blue Letter
- Blue Money
- Blue Sky
- Blue Suiter
- Boca
- Bogey
- Boil the Ocean
- Boiler Plate
- Boolean
- Boolean Operation
- Boot
- Bottleneck
- Box
- BPS
- Bridge
- Broadband
- Broadcast
- Browse
- Browser
- Buck Slip
- Buffer
- Bug
- Build-to-Order
- Build-to-Plan
- Bullet
- Bulletin Board
- Bullets
- Burn
- Burst
- Bus
