In contract bridge the convention of Jacoby transfers is used to describe various types of hands after partner opened 1 No Trump, complementary to the Stayman 2-Club response. Its main purpose is to play the hand in 2 of a major suit (that is spades or hearts) from the strong hand that opened 1NT. But by giving up the natural meaning of the 2 Diamonds response to 1NT (being of limited use, as more frequently overbid by opponents than 2H or 2S) a lot of flexibility is gained.

Furthermore the 2 Spades bid is freed for other uses (e.g. Forcing Baron or minor suit hands)

That is the basic way it works:

After the response of 2 Diamonds or 2 Hearts to an 1 No Trump opening, opener

is requested to bid the next suit (Hearts or Spades).

Then the bidding continues as follows:

• pass shows a weak hand with a long suit (natural as bidding might end)
• 2 No Trumps shows an invitational hand with a five card suit
• 3 In the Transferred Suit (Hearts or Spades) shows an invitational hand with a six card suit
• A new suit is forcing to game at least showing 5-4
• 3NT shows a five card suit with game going values (opener might revert to the major suit game)
• 4 in the transferred suit is to be played
• Jumps in new suits are to be defined in most partnerships (splinter bids, cue bids or extreme 2 suiters are some of the reasonable choices)