Weak Twos are opening bids that show 5-10 points and six cards in the bid suit. Ideally, opener has concentrated strength in his six-card suit and nothing in the other suits. The classic weak two bid looks something like this:

AQJTxx
x
xxx
xxx

By opening 2 you make it harder for the opponents to find a fit in one of the other suits, if they have one.

A weak two bid usually does not contain a side four-card major, although this is up to partnership agreement. The reason it is dangerous to preempt with a side four-card major is because the partnership may miss a good fit in that major, perhaps even a game contract, while they may have no fit in the weak two suit and may languish there.

When responder has a good hand that is at least interested in a game contract, he can respond 2NT, which is artificial and forcing. Responder usually has at least two-card support (otherwise he could have bid a new suit, forcing). Opener is asked to show a feature in a side suit, i.e. an ace or king, by bidding that suit at the three level. Examples:

2 : 2NT
3

3 shows the ace or king of clubs.

2 : 2NT
3

3 shows a minimum hand with no side suit features.

In competition, the artificial 2NT response and rebids are on.

A simple raise of the weak two bid is preemptive and completely nonforcing. Jump raises of a major suit weak two show either a weak, preemptive hand (usually with at least four-card support) or a strong hand that believes the game contract will succeed. Jump raises of 2 are strictly preemptive, usually with at least four-card support.

See also Ogust.