Smolen

Smolen is a variation of Stayman. Without Smolen, if responder to 1N has 5-4 in the majors and bids Stayman, then if opener bids 2, denying a 4-card major, responder would have to bid 3 or 4 of his 5-card major, wrong-siding the contract.

With Smolen, if opener bids 2, the Smolen bidder jumps in his 4-card suit, letting opener know that the other major is his 5-card suit. Opener either bids 3N without 3-card support, or he bids 4 of the 5-card suit. Either way, opener gets to be declarer.

1N - 2
2 - 3 = 5 Spades
Opener bids:
3 with 3 Spades
3N with just 2 Spades

1N - 2
2 - 3 = 5 Hearts.
Opener bids:
4 with 3 Hearts
3N with just 2 Hearts