A cold four-bet is a re-raise made against an initial raise and a three-bet when the player making it has not yet invested in the pot. It signals extreme strength and is often used to apply maximum pressure on aggressive opponents. Effective in deep-stacked play, it can exploit loose three-bettors and force folds from marginal hands. Proper application requires understanding opponent tendencies, stack sizes, and table dynamics to ensure it is not overused or easily countered.