The Rosenkranz redouble is used to distinguish between different types of raises in competitive auctions. When one's partner makes an overcall and the next player (responder) makes a negative double, a redouble is used to show a raise which includes the ace or king in the bid suit; an actual raise shows a similar hand but denies a top honor.
This convention is named after its inventor, George Rosenkranz. Variants include Guildenstern, in which the meanings of the redouble and direct raise are reversed, and Munson,created by Kitty Munson Cooper, in which the redouble shows shortness (one or two cards) including the ace or king.
After a Munson redouble, the overcaller's spot-card lead in his overcalled suit is suit preference for the side suit to shift to. In both cases, the reasoning is that a better hand for the bid suit should raise the level of the auction to make things difficult for the opponents.
The call is analogous to Rosenkranz doubles (also created by George Rosenkranz), that also apply in advancing partner's overcall, where responder has bid a new suit, an auction such as (1C) 1S (2H) Dbl. Like the Rosenkranz redouble, the Rosenkranz double originally showed support (enough strength to raise to 2S) along with the ace, king, or queen of spades; while a direct raise to 2S denied possession of the ace, king, or queen.
Subsequent to creating the Rosenkranz double and redouble, Rosenkranz announced (in a letter published in the ACBL's Bridge Bulletin) that he had adopted the proposal of Eddie Wold's to switch the meaning of the two sequences, so that the advancer's immediate raise to 2S now showed the trump honor, while the double (and redouble) now denied it (i. e., "Reverse Rosenkranz.") The term "Guildenstern" (a reference to Shakespeare's other courtier in the play Hamlet) was used for these sequences in independent creation of "Reverse Rosenkranz."