Definition
A situation in which both players are dealt very strong cards and are forced to get all their chips in, but one of them wins by making a stronger hand. In a cooler both players act absolutely correctly by playing for their whole stack, but because of the luck factor one of them loses and the other wins. For example, Hero is dealt 33 preflop and the flop comes 336, improving his pair to quads. Hero and his opponent get all-in, and the other player turns out to hold pocket 66, which gave him a full house. This is a cooler, because the second player could not avoid calling with a big full house.