Uniform Resource Name
a standard string of characters that allows an object or a service to be accessed over a network
The standard notes the intention "that the lifetime of a URN be permanent. That is, the URN will be globally unique forever, and may well be used as a reference to a resource well beyond the lifetime of the resource it identifies or of any naming authority involved in the assignment of its name." If the location of an object or service changes, it should be possible to locate the object or service through its URN.
RFC 3986, 2005The term "Uniform Resource Name" (URN) has been used historically to refer to both URIs under the "urn" scheme [RFC2141], which are required to remain globally unique and persistent even when the resource ceases to exist or becomes unavailable, and to any other URI with the properties of a name.