Baron is a set of conventions

Bridge convention

A bridge convention is a system of calls made during the auction phase of a contract bridge game which conveys a coded meaning about the players' card holdings...

 in the game of contract bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

. There are three common variations of the Baron convention used in the game.

Baron Three Clubs

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.

Baron Notrump Overcall

A 1NT overcall

Overcall

In contract bridge, an overcall is a bid made after an opening bid has been made by an opponent; the term refers only to the first such bid. A direct overcall is a bid made directly over the opening bid by right-hand opponent; an overcall in the 'last seat' is referred to as a balancing...

is used over an opponent's opening suit bid and shows a weak hand with support for the unbid suits (i.e. it excludes support in the opponent's suit).

Baron Two Notrump Response

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.