Meaning of rule of eleven

rule' of elev'en

Pronunciation: [key]
— Bridge, Whist. Bridge,Whist.
  1. the rule that when a player leads his or her fourth-highest card in any suit its numerical value subtracted from eleven gives the number of higher cards of that suit held by the other players.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.