Participant means everyone who is part of the webinar except the one Organizer. This is the maximum number of people of all categories who are connected to the webinar. My plan has a maximum of 500 participants, which means that I can have 501 total people connected to the webinar including myself, the Organizer. Think of this as everyone at a banquet except the Organizer, who is too busy to really enjoy the banquet.
GoToWebinar uses the term Attendee for people who attend in the webinar and probably do not speak during the webinar. Think of this as the audience at a banquet.
A Panelist is a special category that is usually used for the group of people who will be presenting during the webinar. During the webinar an Attendee can be promoted to become a Panelist. Think of this as the head table at a banquet.
Organizer is the person who created and started the webinar and keeps it going. They might not ever speak during the webinar. They have control over who is allowed to speak and what is shown on the screen. Think of this as the person in charge of the banquet who is running around making sure everything is perfect and that everyone is having a great time.
Co-Organizer is a unofficial term for people who have almost the same rights as an Organizer, but GoToWebinar calls them Organizer. They assist the Organizer and are counted in the total number of Participants.
