“A Uniform Resource Identifier (URI), is a compact string of characters used to identify or name a resource. The main purpose of this identification is to enable interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. URIs are defined in schemes defining a specific syntax and associated protocols.” (Wikipedia)

The most common URI is a URL, or Uniform Resource Locator, which both identifies a resource and describes how to find it. The URN, or Uniform Resource Name, names a resource without giving location information.