Have you encountered yourselves hesitating when trying to use the terms URI or URL? I have. Apparently the difference between a URI and a URL is a very debated topic on the web. And it's also a source of confusion for many people, including myself.
Almost every comparison that I find seem to be a tongue-twister, which vaguely describes that they are related but they're not the same (aha! you see? I did it too, I said something but actually said nothing. PLOP!). The truth is that there's a different RFC describing the scheme of each, URI's and URL's. If you go through the W3C documentation you'll find that they have a documentation page trying to clarify the confusion around URI's.