Definitions of Seminar, Workshop, Symposium and Conference
Seminars are educational events that feature one or more subject matter experts delivering information primarily via lecture and discussion. A seminar is often one person giving perhaps an hour-long lecture, although there could be more than one speaker as well.
A workshop has the sense of being a relatively small event with all parties involved in the discussion (although this is not always the case). Workshops tend to be smaller and more intense than seminars. This format often involves students practicing their new skills during the event under the watchful eye of the instructor.
A symposium suggests that more than one person is speaking. A Symposium is typically a more formal or academic gathering, featuring multiple experts delivering short presentations on a particular topic.
A conference is pretty general and in fact could mean something with thousands of participants or something with just a few participants. None of these are hard and fast rules though. Conferences often features keynote presentations delivered to all attendees, as well as multiple break-out sessions. Attendees often expect to receive information about industry trends and developments.