UDP
User Datagram Protocol. One of the protocols for data transfer that is part of the TCP/IP suite of protocols. UDP is a “stateless” protocol in that UDP makes no provision for acknowledgement of packets received.

Unique Visitors
A unique visitor refers to each different person visiting your site during the given period which the unique visitor figure is reported.

Different measurement periods will give rise to terms like Daily Unique Visitors and Monthly Unique visitors.

The unique visitor figures are usually reported by web stats program offered with the hosting package.

UNIX
A computer operating system (the basic software running on a computer, underneath things like word processors and spreadsheets), first developed by AT&T Bell Laboratories in the 1970s and then licensed to many universities. UNIX is designed to be used by many people at the same time (it is multi-user) and has TCP/IP built-in. A basis for Linux, it is the most common operating system for servers on the Internet.

Upload
Refers to the act of putting a file onto a web server so that it can be accessed by other people.

UPS
Uninterrupted Power Supply. Used commonly for servers to ensure zero downtimes due to power failures.

Uptime
Measure of the time period which the web server has been online. For example, a server can have an uptime of 100 days - meaning it has not failed during the last 100 days and has ran non-stop during that period.

URL
Uniform Resource Locator. The standard way to give the address of any resource on the Internet that is part of the World Wide Web (WWW). A URL looks like this: http://www.top10cheapwebhosting.com/index.html

The most common way to use a URL is to enter into a WWW browser program, such as Netscape, or Lynx.

Usenet
Network of all the newsgroups in the Internet.

UUencode
It is a method of sending binary files using email - similar in purpose to MIME.