RPI supplies two predefined system user groups: System Administrators and Everyone. Predefined groups are read-only and may not be deleted.
The System Administrators group is associated with all functional permissions. The Everyone group is associated with no functional permissions.
You cannot add a user group with the same name as a predefined user group.
By default, a newly-created user is added automatically to the Everyone user group. It is not possible to remove a user's membership of the Everyone user group.