Lecture: A class where students take notes from what is being 'lectured' to them by a subject tutor. The most typical form of teaching at university.
Seminar: A class where debates and dialogue is encouraged, the exchange of ideas and the formation of arguments, facilitated by a tutor. Almost like a conference or rather a group meeting for discussion.
Tutorial: A one-on-one or a very small group session with a given tutor.
Semester: A half-year term at University.