URI

Every resource available on the Web -- HTML document, image, video clip, program, etc. -- has an address that may be encoded by a Universal Resource Identifier, or "URI".

URIs typically consist of three pieces:

The naming scheme of the mechanism used to access the resource. The name of the machine hosting the resource. The name of the resource itself, given as a path.

Source: http://www.w3.org/TR/html401/intro/intro.html