Uniform Resource Locator

What is an URL

An Uniform Resource Locator (URL) is the term used to identify an Internet resource, and can be specified in a single line of text.

What is an URN

An Uniform Resource Name (URN) is the term used to identify an Internet resource, without the use of a scheme, and can be specified in a single line of text.

What is an URI

An Uniform Resource Identifier (URI) is used by a browser to identify a single document, and it too can be specified in a single line of text.

URL vs. URN vs. URI

The difference between the three is subtle. An URL refers to a Web page, including the scheme, but without a name location. An URN may also include the location of a code fragment. An URI refers to a Web page including the location of the code fragment, if one exists, and the scheme.

URL	http://www.pierobon.org/iis/review1.htm
URN	www.pierobon.org/iis/review1.htm#one
URI	http://www.pierobon.org/iis/review1.htm.html#one

Because Web servers allow for default documents and do not require a scheme to retrieve a document, the subtle difference between an URL and an URN and an URI is hard to tell. URL is now used as the generic term.

Additional information on URL specification may be found here.