The term is also used in draw poker to denote an unmatched card (often an ace) retained by a player during the draw in the hope that either it will be paired on the draw, or else play as a kicker (in the first sense) on the showdown.
Kickers take on special importance in Texas Hold'em, because a common winning hand is one pair of a card in a player's hand matched with a card on the board, while the player's second card acts as a kicker. For example, if one player holds A-Q, a second player holds A-10, and the board is A-J-8-5-3, the player with the Q kicker wins because A-A-Q-J-8 defeats A-A-J-10-8. If the board, however, were A-K-5-9-5, the players would tie, because both would play the hand A-A-5-5-K; in this case it is said that the players' kickers "don't play", or that the "kicker on the board plays".