There can be up to 3 types of users on a group's admin team.
Here is what each of them is able to do:
Group Admin: Has access to most member and forum management functions (accepting applications, deleting posts, etc.), but not overall group settings. She also has ability to feature posts. Each group can have any number of Admins.
Group Head Admin: Has almost all permissions Group Owners currently have, including access to most group preferences and managing a group's admins. Each group can have any number of Head Admins.
Group Owner: Can transfer group ownership, manage head admins, view removed members, and update member maintenance settings. Each group can only have one Group Owner.