URI stands for Uniform Resource Identifier, the official name for those things you see all the time on the Web that begin 'http:' or 'mailto:', for example http://www.w3.org/, which is the URI for the home page of the World Wide Web Consortium. Historically, URIs were mostly seen as simply the way you accessed Web pages. These pages were hand-authored, relatively stable and simply shipped out on demand. More and more often that is no longer the case; in at least three different ways:

  • Web pages for reading have been complemented by pictures for viewing, videos for watching and music for listening;
  • The Web is now more than a conduit for information, it is a means to a variety of ends; we use it to do things: purchase goods and services, contribute to forums, play games;
  • The things we access on the Web are often not hand-authored or stable, but are automatically synthesized from 'deeper' data sources on demand. Furthermore, that synthesis is increasingly influenced by aspects of the way we initiate the access.

To paraphrase the World Wide Web Consortium, Internet space is inhabited by many points of content. A URI is the way you identify any of those points of content, whether it be a page of text, a video or sound clip, a still or animated image, or a program. The most common form of URI is the Web page address, which is a particular form or subset of URI called a Uniform Resource Locator (URL).

Additional Reading
What is a SIP URI?
What is a SIP Client?