The word "webinar" is a mix of two ideas: using the "web" to deliver a "seminar".
Before web-based platforms were developed to deliver webinars, like live streaming video conferencing, most companies developed seminars as face-to-face events. Seminar organizers booked a venue, and attendees had to physically go to that location.
Live Online courses (webinars) are a different type of event. Webinar organizers who host webinars can invite people living anywhere in the world the opportunity to participate at the same time.
In this example, webinar platform software allows the host to present a virtual course to attendees in their home/office.