A 2♣ response to a 1NT opening bid, used to enquire about major-suit holdings. In reply, opener rebids:
2♦ No four-card major.
2♥ Four hearts (and possibly four spades).
2♠ Four spades.
With the first responding hand, you have the values to raise 1NT to 3NT but want to play in a 4-4 fit in a major if one exists. You intend to raise 2♥ to 4♥, 2♠ to 4♠ or to jump to 3NT over 2♦. On the second hand, you use Stayman intending to pass at your next turn, confident that a suit contract will play better than 1NT.
Responder can safely use Stayman on any hand with the values to bid at least 2NT and four cards in at least one major. Depending upon the partnership methods, responder may also be able to use Stayman on other hand types (such as a weak hand with both majors or a weak single-suited club hand).