Meaning of long suit

long' suit'

Pronunciation: [key]
    1. the suit in which the most cards are held in a hand.
    2. (in bridge) a suit in which four or more cards are held in a hand.
  1. the quality, activity, endeavor, etc., in which one excels: Diligence is his long suit.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.