A seminar means a class or meeting, but it carries with it extra weight. An educational seminar indicates a small, advanced study, while a meeting labeled as such means an intense exchange of ideas.
The Latin seminarium originally referred to a plant nursery, a place of great growth. From this came the German seminar, referring to a formal educational group led by a professor. While university seminars are most frequently small-group studies of a particular issue, the word is also applied to large lectures and commercial pitches. Like the seminar you attended on how to get rich by selling carrot peelers to your neighbors.