Acronym for Uniform Resource Name. Like an URL, an URN is a short, unique string used to identify a resource on the Internet. Unlike an URL, an URN does not necessarily specify a particular location for a resource; an external mechanism resolves the URN to a location for accessing the resource. Thus, theoretically, a link to an URN will survive any relocation of the named resource and avoid the all-too-common 404 errors encountered on the Web today.
IETF documents defining aspects of URNs include RFC 2141 ("URN Syntax"), RFC 2169 ("A Trivial Convention for using HTTP in URN Resolution"), RFC 2483 ("URI Resolution Services Necessary for URN Resolution"), and RFC 2611 ("URN Namespace Definition Mechanisms").
See also: URI.