Baron is a set of conventions in the game of contract bridge. There are four common variations of the Baron convention used in the game. They arise from the Baron bidding system developed in Britain from the 1940s as a variant of Acol.
The Baron Three Clubs is an alternative to the responder using Stayman over a 2NT opening bid. The responder will have 5 points or more and an unbalanced hand. The responder bids 3 clubs, which asks opener to bid his four card suits in ascending order. If clubs are the only 4 card suit, the opener then bids 3NT.
If there are two 4-card suits (one being clubs), the opener bids the higher first (then) 3NT for the clubs if no fit is found. The opener's 2NT is a limited bid and the responder has not shown the strength of his hand, therefore the responder will control how high the bidding goes, game or prospecting for a slam, and the suit to be played. The main advantage of this convention is that it becomes easier to reach minor-suit slams.
A 1NT overcall is used over an opponent's opening suit bid to show a weak hand with support for the unbid suits (i.e. it excludes support in the opponent's suit).
When the opening is a bid of one of a suit, a 2NT response is given showing 16-18 points and a generally flat hand. 3NT shows 13-15 points. This is also known as the Two NoTrump Forcing Response.
After a 1NT opening, a 2S response asks opener whether he is minimum or maximum for his bid. Opener responds 2NT with a minimum or 3 of his lowest 4 card suit with a maximum. Responder may have one of two ranges; 11-12 points (looking for game in NT) or 17-20 points (looking for slam in NT or a minor suit). Similarly after a 2NT opening, 3S asks opener whether he is minimum or maximum, looking for a slam.