Webinars are 1-2 hour online events that are structured similar to a seminar, with the majority of the time having speakers present information and/or conduct demonstrations.
Webinars do not have a maximum number of participants.
Workshops are 1-2 hour online events that are structured to deliver information but also have the audience engage in intensive discussion on a particular subject. This could include the use of breakout rooms for small group discussion, polling, quizzes, etc...
Workshops tend to have 25-50 participants.