Stayman
Stayman is used to try to locate 4-4 fit in major after NT - opening
After 1NT , 2C = Stayman
2D = no 4 c major
2H = 4c hearts (may also have 4c spades)
2S = 4c spades, (denying 4c hearts)
 
Example 1:
A K 5 4 Q J 8 2
K 9 8 A 3
Q 9 7 4 A 8 5 2
A 3 9 8 5
 
1NT = 15-17 2C = Stayman
2S = 4 c spades 4S
pass  
 
Example 2:
A Q 4 2 K 9 8 7
K Q 3 2 A 3 2
A 3 Q J 8 2
9 7 5 8 2
 
1NT 2C = Stayman
2H 3NT
4S pass