The Blizz meeting ID is a unique identifier to determine meetings. Everybody who wants to join a Blizz Meeting requires a Meeting ID.
If you sign up for a Blizz account, you will receive a personal Meeting ID (static ID). If you log in with your account and start a spontaneous meeting, the personal Meeting ID is used automatically. Others can also reach you using this ID.
If you however schedule a Meeting, every scheduled meeting uses its own ID that are different from each other.
If you are not logged in with your account and start a spontaneous meeting, also a different ID is used. However, this ID is unique for every device and does not change.