Member

- Normal member of a Plone site

Group (Team)

- A group in the sense of GroupUserFolder

GroupSpace (Team Folder, CollabSpace, Workgroup)

- A place where members can share content and work together

GroupMember (Or Participant)

- Can see everything and can create content in special workspaces, post
  messages in discussion groups and so on

- GroupMembers can be groups or members

GroupReviewer (Or GroupModerator)

- can review content in the GroupSpace

GroupVisitor

- can see certain things in a GroupSpace, depending on its policies

GroupController

- can see everything

GroupAdmin (Or GroupManager, Staff, Admin)

- Manages the GroupSpace and assigns GroupMembers to groups.