A seminar is a training session which is held to discuss something. The seminar can last up to three to four hours and have only one session. There can be 50 to 60 students in that one session. A seminar is not driven by the professor, but the students take an active part in the discussion, and the professor just has to oversee the discussion. Though a seminar can have hundreds of students, if it is only held for college purposes, it only includes only a professor and only 20 students.