Kicker
The highest extra card in your hand that doesn't participate in a straight or flush. The card does not contribute to the strength of your hand except by itself.

For example, if you hold KK88A, you have two pair, kings and eights with an ace kicker. Five-card hands (straights, flushes, and full houses) don't have kickers. In games that have community cards kickers can be very important as it is easy for two players to hold similar hands. For example, if you hold KQ and someone else holds KJ, and the flop is AK975, you have your opponent out-kicked. Your hand is AKKQ9 while theirs is AKKJ9.