Gerber_convention
Gerber convention
Slam bidding convention in contract bridge
Gerber is a contract bridge convention devised by William Konigsberger and Win Nye from Switzerland[1] who published it in 1936; John Gerber of Texas introduced it to North America in 1938 where it was named after him.[2][3] It is similar to Blackwood but uses 4♣ instead of 4NT as a relay (asking) bid to inquire about the number of aces held by partner. A further relay bid may follow to inquire about the number of kings held.
Gerber is used primarily after notrump openings, responses, and rebids, making it a complement to Blackwood rather than a replacement. Some club players also use it after suit bidding, but most experts do not recommend this.