Undo A function in some programs that allows you to reverse tasks. Word, for example, also has a Redo option

Uninstall To remove programs from the PCs hard disk. Software is available for uninstalling programs that do not contain an inbuilt uninstall option 

Upgrade To imprve the performance or specification of a PC by adding new hardware, such as a higher capacity disk drive, or software. See Hardware,Software 

URL Uniform Resource Locater. A standard style used for all Internet addresses on the World Wide Web. The first part of the URL, such as (for example) www.yahoo.com, indicates the location of a computer on the internet. Anything thast follows, such as/homhtm,gives the location of a particular file on that computer.

USB Universal Serial Bus. A hardware connector that allows users to plug a wide range of USB devices into a computer without having to restart. See Hardware 

Utilities Software that assists in certain computer functions, such as uninstalling and virus-scanning.