Kicker

Button holds K-Q, the big blind defends with K-9. The flop comes K-8-4 and both players pair the king. The turn and river bring two low cards that change nothing, so at showdown both hands show a pair of kings. It comes down to the next card in line: queen beats nine, and the button wins with a card that never got mentioned during the betting.

That is the whole job of a kicker. Any time two players make the same pair, the side card settles it. Top pair with a strong kicker beats top pair with a weak one about three times in four when both hands reach showdown, and on a dry board that gap is often the whole edge. A player who thinks "I paired the board" and stops there is reading half his hand.

The beginner mistake is playing weak-kicker hands like A-5 offsuit or K-3 offsuit because an ace is an ace and a king is a king. Pair the top card, feel good, then run into A-K or K-Q and lose a full pot instead of ever being close to a chop. The fix: before you call a raise with a weak kicker, ask what the raiser is likely to pair with, and whether your side card still wins when you both get there.