Smolen
The Smolen convention is an extension of Standard Stayman for situations in which the responder has five cards of one major and four cards of the other, with game-going values. If the notrump opener responds to the 2♣ (3♣) response with 2♦ (3♦) to deny a four-card major, the responder bids three of the four-card major. The notrump bidder then places the contract by bidding four of the other major with three cards in the suit or 3NT with fewer than three. This convention allows a partnership to find either a 4-4 fit or a 5-3 fit while ensuring that the notrump opener, who has the stronger hand, will declare the contract in any case.
Read more about this topic: Stayman Convention