Wiktionary
n. A strategy, in pontoon or blackjack, in which a player keeps a mental tally of the cards played in order to calculate the probability of certain cards being dealt and therefore obtain an advantage.
Wikipedia
Card counting is a casino card game strategy used primarily in the blackjack family of casino games to determine whether the next hand is likely to give a probable advantage to the player or to the dealer. Card counters are a class of advantage players, who attempt to decrease the inherent casino house edge by keeping a running tally of all high and low valued cards seen by the player. Card counting allows players to bet more with less risk when the count gives an advantage as well as minimize losses during an unfavorable count. Card counting also provides the ability to alter playing decisions based on the composition of remaining cards.
Card counting, also referred to as card reading, often refers to obtaining a sufficient count on the number, distribution and high-card location of cards in trick-taking games such as contract bridge or spades to optimize the winning of tricks.
Usage examples of "card counting".
The secret mechanics of The System were hopelessly intricate, its parlance -- splitting, doubling down, hi-lo differential -- an insider's code, but the mainspring seemed to involve a species of card counting, a task Jessie could hardly imagine Dow mastering since whatever stores of patience and concentration he had managed to haul down with him from the north country had been thoroughly consumed out here in the great southwestern fry pan of loss and disappointment.