Meetings in Teams include audio, video, and screen sharing for up to 1,000 people and a view-only streaming experience for participants over 1,000. Participants don't need to be a member of an organization (or have a Teams account) to join a Teams meeting. They can join directly from the calendar invitation via the Join meeting link or call in via audio if available (limited based on need)
In addition to regularly scheduled meetings, your users can create channel meetings. With channel meetings, everybody in a team can see there's a meeting, join the meeting, and use the meeting chat.
Meetings are generally best for situations where participants need to interact with each other via voice or chat and where multiple people may be presenting.
Webinars are structured meetings where presenters and participants have clear roles. A key difference between webinars and Teams meetings is that webinars support robust registration management, a customizable event and registration site, and event-oriented default meeting options.
Town halls are generally best for situations where a limited number of presenters are presenting to a large group of attendees and direct interaction via chat or voice conversation isn't needed. For these event formats, attendees don't use their cameras and mics, but instead use Q&A to engage with presenters and organizers.