I know that ゼミ is short for ゼミナール (seminar), but the word seems to be used differently than how it's used in English. My guess from the times I've seen it used is that it's a catch-all term for university classes, is that correct?
I don't think it's quite a catch-all phrase, but I guess people may use ゼミ for smaller specialized classes with more professor–student interaction, even if the professor actually gives all the lectures/talks. (I guess in this case you would use "course" and not "seminar" in English.)
I don't think ゼミ would be used for the main compulsory classes in an undergraduate programme.