The System Administrator
The user who is the System Administrator automatically receives full access rights in all the applications. They are the only one who can add new users as well as determine what access rights the other users have in the applications. This is usually the first user in the application.
The Application Administrator
The user who is an Application Administrator can determine what access rights the other users have in the application they are the administrator for. The Application Administrator automatically receives full rights to the applications they are an administrator for, but cannot add users.