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Cue Bidding
Cue Bidding

Cue bidding takes place when a suit has been agreed and one partner is looking for a slam. e,g, 1♠ -3♠ - a bid of 4♣  shows a control. If the 3♠  bidding hand has a control they may bid there next control upwards. e.g. 4  which gives the opener information that responder does not have a control in  s, but has one in  s, Wth this information he can use Blackwood or siign off in game.

The main choice and agree with your partner is whether the cue bid show 1st round control (Ace or void) or both 1st and 2nd (Ace,, non singleton K, void or singleton). 

For more information see this link on Cue Bidding..