Relatively full overview of what a group is, how they are nested, group types, etc
FROM GROUP FEATURES (and rewritten)
A group is a logical container of members with similar requirements or interests (for example, your company's product). A group is also a mechanism that contains and organizes different types of communications the members can use: forums, blogs, wikis, or galleries. The applications have no relationship with each other within the group.
To picture this, think of the people in your organization, then mentally organize them into functional groups and identify their communication needs. For example, you might have a Product Group in your organization that makes announcements (blogs); writes documentation (wikis); provides downloads (galleries); and fields support requests (forums).
FROM THE CONTENT MODEL:
In the most logical, simple way, a group is a container which can hold other containers. Containers can be nested within themselves to provide deep navigational structures.
FROM GROUP FEATURES
Groups also have types, which govern the way the group can behave regarding membership. The types include:
- Private Unlisted - Community users can't see this group's activity or users.
- Private Listed - Community users can see users and group activity, but can't participate in group activity.
- Public Closed - Community members can see group activity and additional group information in the sidebar, but can't see the activity of group members.
- Public Open - Community members can see group members and activity. Additional group information is visible in the sidebar.
- Joinless - Membership isn't tracked (i.e.there are no members). Site-level roles control the group's permissions using site-level permissions. Joinless groups are managed by system administrators unless an administrator creates a special role for managing this group.
Within a group container, there are three levels of membership: Group members (can create and view group content, view group members, and invite prospective members); Group managers (have the same permission as group members, but additionally can manage the group); and Group owners (have the same permissions a manager but also can control group settings, add new members, modify the group theme, create new applications, create new roles, and and modify role permissions.