The Rule of 11 is used for declarer play (or defense) at trick one. It assumes that the opening lead was "4th-best."
It is usually used at notrump, when the lead is assumed to be the 4th-highest card in the suit. By subtracting from 11, the declarer can tell how many cards higher than the card led are in the other three hands. For example:
...
J1087 
KQ109763 
A3 
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