A version of Stayman for five-card and four-card suits following an opening bid of 1NT or 2NT. After 2NT-Pass- 3♣-Pass-3♦ (denying a five-card major), responder bids the major in which he does not hold four cards.
The main purpose of bidding the major he does not hold is that the strong opening hand will become declarer if a fit is present.
For example:
A heart lead would put 4♠ from the East seat in jeopardy.
With West as declarer, there is the chance of playing three rounds of diamonds to discard a heart from the East hand.