According to RFC 3986:
A URI can be further classified as a locator, a name, or both. The term “Uniform Resource Locator” (URL) refers to the subset of URIs that, in addition to identifying a resource, provide a means of locating the resource by describing its primary access mechanism (e.g., its network “location”). The 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.
In Simple Words…
Consider a specific edition of Shakespeare’s play Romeo and Juliet, of which you have a digital copy on your home network.
You could identify the text as
urn: ISBN: 0-486-27557-4.
That would be a URI, but more specifically a URN because it names the text.
You could also identify the text as
That would also be a URI, but more specifically a URL because it locates the text.
- Bruce Wayne
This is my name, which is identification. It is like a URI, but cannot be a URL, as it tells you nothing about his location or how to contact him. In this case it also happens to identify at least 5 other people in the USA alone.
- 4914 Wayne Manor, Gotham City, USA
This is a location, which is identification for that physical location. It is like both a URL and URI (since all URLs are URIs), and also identifies me indirectly as “resident of…”.