Response of 2C to partner's one notrump opening, asking opener to bid a four-card major if she has one. Opener bids 2 diamonds to deny a four
card major. If responder bids a major, he is showing at least 5 cards in that major.. Invented by Samual Stayman. There are two
versions of Stayman:
a) Forcing Stayman -- responder's rebid of two in a major suit is forcing on opener to bid again.
b) Non-forcing Stayman - responder's rebid of two in a major is not forcing. To make a forcing bids, responder must bid again at the 3 level.