This is an important convention that comes in handy.
Responder’s Second Bid
Modern bidding has a problem-child:
♠ Q 8 7 North South
♥ A Q 9 8 7 1♦ 1♥
♦ K J 6 1♠ ??
♣ 5 4
South has a problem: He wants to bid NT, but not without a stopper in clubs, the only unbid suit. He should not jump in his 5-card heart suit (only perverts do that), and he should not raise opener’s second suit with only 3-card support. There is a nice solution to this dilemma:
South simply bids the fourth suit, clubs. He bids 2♣ which is forcing (actually any new suit responder bids is forcing), but all-important, it is artificial. Responder does not need anything in the fourth suit. It simply says, Partner, I have a hand good enough for game (13+), but I have no convenient rebid to make, so I’m tossing it back to you.
♠ K 8 North South
♥ A J 5 4 3 2 1♣ 1♥
♦ 9 6 1♠ ??
♣ K J 6
South should bid 2♦ - fourth-suit forcing and artificial.
Again, South has a problem. Now he can rebid his 6-card heart suit, but a jump to 3♥ would only show 11-12 points and could be passed by North. Jumping to 4♥ when North might be void in hearts is not appealing.