http://technet.microsoft.com/en-us/library/dd335146.aspx
Management role scopes enable you to define the specific scope of impact or influence of a management role when a management role assignment is created. When you apply a scope, the role assignee assigned to the role can only modify the objects contained within that scope. A role assignee can be a management role group, management role, management role assignment policy, user, or a universal security group (USG)