- U/L Universal/Local
- UA Unnumbered Acknowledgment / User Agent
- UAE Unrecoverable Application Error
- UART Universal Asynchronous Receiver/Transmitter
- UDP User Datagram Protocol
- UI Uncheck Item
- ULP Upper Layer Protocols
- UMB Upper Memory Blocks
- UNMA Unified Network Management Architecture
- UPS Uninterruptable Power Supply
- URL Uniform Resource Locator
- USL Unix Systems Lab
- UTC Universal Time Coordinated
- UTP Unshielded Twisted Pair
- UUCP UNIX to UNIX Copy Program
- UV-EPROM Ultra Violet Erasable Programmable Read Only Memory
- UVGA Ultra-Video Graphics Array