A splinter bid is a convention whereby a double jump bid in a side-suit indicates a trump fit and a singleton or void in the suit bid. For example, a 4 clubs response to a 1 heart 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 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 high card points 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.
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.
[Source for above material: Wikipedia contributors. "Splinter bid." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 23 Mar. 2013. Web. 9 Apr. 2013.]
The splinter can be used in a variety of situations. The most common are:
West East
1♠ 4♣
East shows a forcing raise that includes club shortage.
West East
1♣ 1♠
4♦
West shows a powerful opening bid (willing to play 4♠ opposite what may be only 6 HCP) with four-card support and diamond shortage.
Splinter bids suggest slam on the basis of fit and distribution rather than high cards. Over a 1♠ opening, responder would try 4♣ on as little as:
♠ Q J 7 4 2
♥ A 8 4
♦ A 10 5 2
♣ 8
Even if opener has a minimum, slam may have a good chance if he has no wasted strength in clubs, as with
♠ A 9 8 5 3
♥ K Q 2
♦ K 4
♣ 9 5 2
Most experts also use splinters in the majors:
West East
1♠ 4♥
If East really had hearts, he could bid 2♥ then 4♥.
West East
1♥ 3♠
If East really had a preempt in spades, he could perhaps bid 1♠ then 2♠ then 3♠.
SOURCE: "Conventions", The Official ACBL Encyclopedia of Bridge, 7th ed. Horn Lake: American Contract Bridge League, Inc., 2011, page 318. Print