Uniform Resource Identifier

A Uniform Resource Identifier (URI), formerly Universal Resource Identifier, is a unique sequence of characters that identifies an abstract or physical resource, such as resources on a webpage, email address, phone number, books, real-world objects such as people and places, and concepts. In particular, the resource need not be retrievable via the Internet, or any computer network.

URIs which provide a means of locating and retrieving information resources on a network (either on the Internet or on another private network, such as a computer file system or an Intranet) are Uniform Resource Locators (URLs). Therefore, URLs are a subset of URIs, i.e. every URL is a URI (and not necessarily the other way around). Other URIs provide only a unique name, without a means of locating or retrieving the resource or information about it; these are Uniform Resource Names (URNs). The web technologies that use URIs are not limited to web browsers.