Josephin 5 NT
Known also as 5 NT Grand Slam Force, developed by Ely Culbertson and dedicated to his wife Josephine. After agreed a trump suit, 5 NT rebid asks the number of top honors (A R D) of the trump. If you have one of them you bid slam, if you have two of them you bid grand slam.
If you do not have any of the top honors, although it is obvious that you will play slam, you should bid 6 Clubs. This is a very useful addition by Italian Bridge Players, because if you bid slam then your partner will raise to grand slam if he needs only one top honor.
You can also use this convention after Blackwood by bidding 6 Clubs for only major trumps. The answer is 6 Diamonds for no top honor, 6 Majors for one, and 7 Majors for two top honors.