From Online Manual
Every member of a forum belongs to a membergroup. A membergroup consists of members that you pick the members to be a part of and you choose the permissions allowed to the membergroup.
There are two types of membergroups:
- Post-Count based membergroup - Where the member's post count determines the membergroup into which the member is placed.
- Regular membergroup - Where allowed members can assign or remove themselves or other members from the group. There are 5 types of regular membergroups:
- Private - Membership must be assigned by a member with the appropriate permission
- Protected - Only administrators can manage and assign
- Requestable - Member may request membership
- Free - Member may leave and join group at will
- Post Based - Member will automatically join this group after making a specified number of posts.