An individual scheme does not have to be classified as being just one
of "name" or "locator". Instances of URIs from any given scheme may
have the characteristics of names or locators or both, often
depending on the persistence and care in the assignment of
identifiers by the naming authority, rather than on any quality of
the scheme. Future specifications and related documentation should
use the general term "URI" rather than the more restrictive terms
"URL" and "URN" [RFC3305].
The classic hierarchy ("URLs and URNs are distinct subsets of URIs") wasn't as neat and useful as originally thought, so "it's just URIs now, with their own scheme-specific qualities" is the modern thinking, as reflected by this passage from RFC3986.
The modern answer to "What's the difference between a URI and URL?" is thus very nearly 'Mu.'
http://www.rfc-editor.org/rfc/rfc3986.txt
From section 1.1.3: