It is a Stayman extension developed by James Sharples ve Robert Sharples to show a special distribution. If it is understood that there is no major fit after Stayman, a minor bid at 4th level shows 4-1-4-4 yada 4-2-3-4 yada 4-2-4-3 distribution. 4 Clubs shows the distributions having 4 cards of Clubs, 4 Diamonds shows the distributions having 4 cards of Diamonds. The aim here is to find a minor fit and to play slam. Otherwise you should play 3 NT.