What is a kicker in Texas Hold'em and how does it impact the outcome of a hand?

In Texas Hold'em, a kicker is the highest unpaired card in a player's hand that is used to break ties between players with the same hand ranking. For example, if two players have a pair of Aces, the player with the higher kicker card will win the hand. Kickers can impact the outcome of a hand by determining the winning player when multiple players have the same hand ranking.