A conventional 2♦ opening bid used to show three or four distinctly different types of hand, including at least one weak and one strong type.
The most popular version of the convention shows either a weak two- bid in a major, or a strong two bid in a minor or a strong balanced hand. Other strong options are a minor two- suited hand and an unspecified three- suited hand (4-4-4-1 or 5-4-4-0).
Responder usually bids 2♥ (or 2♠ if holding support for hearts) to allow opener to clarify which type of hand he holds. Opener passes 2♥ with a weak two in hearts or bids 2♠ with a weak two in spades. Other opener’s rebids over 2♥ show strong hands.