In contract bridge, a splinter bid is a convention whereby a double jump response in a side-suit indicates excellent support for partner's major-suit opening bid (at least four cards), a singleton or void in the side-suit (but not the ace or king) and interest in slam.
The idea was developed independently in 1963 by David Cliff, the first to write about it, and Dorothy Hayden Truscott; it grew out of two earlier bidding tools, the Fragment bid and the Void-Showing bid.
For example, a four clubs (4♣) response to a one heart (1♥) opening establishes hearts as trump suit and indicates a singleton or void in clubs. Most experts agree that a responder should have 10-12 high card points (HCP) for a splinter. With a strong hand, a responder and opener may be able to make slam on sheer strength, so splinters by responder are normally restricted to hands containing 10-12 (HCP) and a void or a small singleton in the splintered suit. A singleton honor is frowned upon. Although they consume bidding space, splinter bids are very descriptive as they help partner to reevaluate his/her hand: soft honors (a king, queen or jack) in the splinter suit lose value, while honors in the other three suits gain value.
In some positions if a simple bid of the suit would be forcing then a single jump can be a splinter. For example, in a system where 1♥-2♣; 2♦ is a forcing sequence, 1♥-2♣; 3♦ may be used as a splinter. (However, this approach would require a specific agreement in advance - many players use this sequence to denote a strong two-suiter.) Some partnerships use certain single jumps as "mini-splinters" that promise less strength, allowing partner to choose between part-score and game rather than between game and slam.
The short suit in a splinter hand is preferably a small singleton, though it can occasionally be a singleton honor or a void. The idea is that partner can easily tell if he has wasted values in the splinter suit; for example, Axxx is ideal whereas KJ9x is almost worthless.
The four diamond bids in the following bidding sequences (with East-West passing throughout) are generally agreed to be splinter bids establishing spades as the trump suit:
A splinter may occur at the three level. In the following auction, South is showing acceptance of hearts and a singleton in spades.