A User who has permission to edit other users, including their "admin settings". Those settings are identified with a "User Admin" badge.
Users with the "User Admin" permission are allowed to edit/moderate all users except the original ‘admin’ user without any restriction.
Where this permission is set
This permission can be set for a User Group in its System Admin Permissions Panel:
Where this permission is used
Tech info
The underlying permission check is $current_User->check_perm( 'users', 'edit' ).