A webinar is a seminar over the web. By holding a conference hosted over the net, a company can save on deployment, or services costs by not having to travel, rent a conference room, and host a seminar. Now they just make a video conference, and if you wish to participate, you log into the webinar.
"If you can't soar with the eagles, then don't fly with the flock!" - Oliver Sykes; Bring Me The Horizon