In community card poker games, top kicker is the best possible kicker to some given hand. Usually it would be an Ace, but with an Ace on the board it would be a King or lower. Having "top pair, top kicker" is frequently enough to win a Texas hold 'em hand.
TOP KICKER
Meaning of TOP KICKER in English
Poker English dictionary. Английский словарь покера. 2012