Ok guys. A superstall is a rear engine high tail (the 727 for example) airplane which tends to suffer a marked nose up pitch after the stall and the wing wake, which has now become low energy turbulent air, passes aft and immerses the high set tail which is in just about the right position to catch it. This greatly reduces the tail effectiveness and makes it incapable of combating the nose up pitch and the airplane continues to pitch up. This pitch up just after the stall is worsened by greatly reduced lift and greatly increased drag which cause a rapidly increasing decent path, thus compounding the rate of increase of incidence. All of this equates to a deep stall with a high angle of incidence.
Read Handling the Big Jets by D.P. Davies Pg. 117-118