What are these buttons called?

They're also sometimes called "chicklets" -- not to be confused with Chiclets, of course.

Other than just calling them buttons - I believe they could be a form of Userbars, however I cannot find a definitive definition of a Userbar.

You could use those for other purposes than buttons. You could simply use them as "designed for: " notes on a page. You could simply use them as pictures for some reason or another. And anything else you can think of. I think the official name would depend on the use.