A Uniform Resource Identifier (URI) is a string of characters that unambiguously identifies a particular resource. To guarantee uniformity, all URIs follow a predefined set of syntax rules, but also maintain extensibility through a separately defined hierarchical naming scheme (e.g., http://). Such identification enables interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. The most common form of URI is the Uniform Resource Locator (URL), frequently referred to informally as a web address. (Definition source: Wikipedia.)