A Joomla user group collects accounts that share access rules. One user can belong to several groups.
Groups and permissions
Groups form a hierarchy and participate in Joomla permission inheritance. An editorial group can be allowed to edit articles without accessing system configuration. Effective permissions depend on all memberships and applicable denials.
Groups and visibility
A viewing access level lists the groups allowed to see an item. A Joomla group’s name does not define its permissions. Check settings and calculated results, especially after changing a parent group.
Create groups around working roles. Test Joomla access with a separate account rather than assuming that a label such as Editor guarantees the required behaviour.