Here you can add, edit and delete special groups.

8-Groups 8-Groups-Options-1

Default Joomla! groups can not be edited or deleted. The purpose of this protection is to offer you the possibility to remove AceACL later and continue running your site without any issue.

AceACL creates the Guest & Super User special groups automatically. As you can understand from their names, the "Guest" group offers you the possibility to assign permissions to visitors not logged in and the "Super User" offers you the possibility to allow any user to DO EVERYTHING without any Access Control.

As mentioned in this article, there is NO GROUP INHERITANCE and AceACL uses groups just to categorize users and the name of the group does not matter in any way. Another important point is that if one group gives you access then you are in.