There are two types of meeting IDs: Personal Meeting IDs and One-time Meeting IDs.

Using a Personal Meeting ID is similar to using a traditional meeting bridge. It's a convenient way to schedule meetings, because you don't have to remember meeting details for each new meeting that you schedule. To  set them up, add as a meeting attendee in your meeting invite. This type   of meeting is more open, and should not be use for confidential or back-to-back meetings.

One-time Meeting ID is a unique ID used for individual meetings or a meeting series. This ensures that meeting attendees have dial-in information specific to the meeting or meeting series, preventing back-to-back meetings from merging. These are ideal for confidential, overlapping, and back-to-back meetings.