Circles have an aim, a domain and clear membership. They will typically meet to coordinate their operations and to make policy decisions. Meetings can be circle meetings, but meetings can also just be gatherings of groups other than circles. For example, a non-decision making group (like a community practice) or an interest group (like in Open Space) can meet. In that case, a meeting wouldn’t be a circle meeting.
For more information, check out our handbook Many Voices One Song section 2.7.1