Bruce, when I first learned that rule, it was, "Cover the last honor lead from dummy."

 

For example,

    QJ9

 

10xx    Kxxx

 

    Axx

 

Declarer leads the Q, you don't cover. Wait for the J "Last honor". If you cover the Q, declarer can finesse the 10 from partner, picking up 3 tricks. If you wait for the J, declarer only gets 2 tricks.