The weak two bid is a common treatment used in the game of contract bridge, where an opening bid of two diamonds, hearts or spades signifies a weak hand with a long suit. It is used in combination with the strong two clubs bid and is a form of preemptive bid. The term refers to an opening bid, and is not to be confused with the "weak jump overcall", which denotes a similar type of hand, but is bid over an opponent's opening bid.
The requirements for a weak two bid may vary by partnership agreement. The most common treatment is that it requires:
What constitutes a "good" suit is again a matter of partnership agreement. The American Contract Bridge League recommends that the opener hold at least two of the top three or three of the top five cards in the suit (that is, either K-Q or Q-J-10 or better). Others recommend at least three honors (J-Q-K).
A prototype of the weak two was used in auction bridge, and the principle was attested as early as 1910 by J.B. Elwell. It was incorporated into the Vanderbilt Club system. In early 1940s, Howard Schenken developed the modern weak two-bid along lines similar to Vanderbilt's.
In Charles Goren's original bidding system, when a player opened the bidding with two of a suit, this signified that the player held a very strong hand. (This later became known as the strong two bid.) Later players found it more effective to reserve only the conventional two clubs opening; to show a strong hand. That left the room for opening bids of 2♦, 2♥, or 2♠ to show a weak hand with a six-card suit. This became known as the weak two bid. In some systems, a bid of 2♣ shows a strong hand with a five-card suit, and a bid of 2♦ shows a hand that is similarly strong, but balanced. These alternate versions are less common.
Standard American and Standard English Acol responses to weak twos are as follows...
This is known as RONF for raise only non-forcing bid.
After a 2NT enquiry.
Some pairs play a feature shows a stop for NT.
Playing Parallel Twos an opening 2♣ shows five hearts 7-11 HCP, 2♦ shows five spades 7-11 HCP. The 2♣ and 2♦ opener's are referred to as Parallel Twos because they are played in parallel with the regular six card weak twos in hearts and spades. You can play them in any bidding system Acol, SAYC, Precision, Blue Club etc. See the eBook "Parallel Twos For You" N.Jones June 2014.