URI?

I am a relative newb in re: webmastering. I visited the HTML
validator page; had it review my home page and got some useful feedback. I have one question at this point and swear I am not trying to be a smart aleck. Is URI (as opposed to URL) a typo or is this there an acronym I am not familiar with?
Michael Hutchison
L & M Graphic Design
Mail2@lmgraphicdesigns.com