Definition of kicker
A kicker is an acolyte. The sidekick is used to split the prize pool when two players have the same pair. For example, if two players are down on 2-7-A-3-8, the player with AK will have a pair of aces and a kicker king and the player with AQ will have a pair of aces and a kicker queen. The player with AK will win the jackpot with his sidekick (kicker). There are always 5 cards in a Hold'em hand. If our two players previously with AK and AQ were now on a 5-5-6-7 board, it looks like each player has 2 pairs (a pair of 5s and a pair of 6s) with a kicker ace for the fifth card. Now the king and queen would no longer be considered.
The importance of the kickers
One of the mistakes beginners make at the beginning is not to consider the kickers. This is a mistake that causes them to lose a lot of money. If you have a hand like A2 on A-5-5 and your opponent bets, it's okay to call. If the turn is an 8 and he's still betting, you can think about it, but let's say you call again. And if the river is a 9 and he still bets, it's very likely that our opponent has a better kicker than your 2 here and calling all 3 bets with a simple pair of aces and a bad kicker is certainly a loser versus the majority of the bad guys.