Hole carding refers to obtaining knowledge of cards that are supposed to be hidden from view in card games. The term is usually applied to blackjack

Blackjack

Blackjack, also known as Twenty-one or Vingt-et-un , is the most widely played casino banking game in the world...

 but can apply to other games with hidden hole cards, like three card poker

Three card poker

Poker played with three cards dates back to the origins of the game of poker. As a result it's as unclear as the origins of poker, but includes the 16th century British card game of Brag. Rules for three card poker are included in Hoyle's Rules of Games from 1983 along with a hi-low...

 and Caribbean stud poker

Caribbean stud poker

Caribbean Stud poker is a casino table game with rules similar to five-card stud poker. However, unlike standard poker games, Caribbean stud is played against the house rather than against other players...

. So long as it does not involve the use of a device like a mirror or actions like touching the dealer's cards, in most jurisdictions hole carding is a legal form of advantage gambling

Advantage gambling

Advantage gambling, or advantage play, refers to a practice of using legal ways to gain a mathematical advantage while gambling. The term usually refers to house-banked games, but can also refer to games played against other players, such as poker...

 in casino table games. In other games, like stud poker

Stud poker

Stud poker is any of a number of poker variants in which each player receives a mix of face-down and face-up cards dealt in multiple betting rounds. Stud games are also typically non-positional games, meaning that the player who bets first on each round may change from round to round...

, casinos normally have rules against rubbernecking or having a confederate stand behind an opponent to signal hole cards.

Blackjack players must usually make playing decisions based on only seeing one of the dealer's cards (the upcard). But if the dealer's hole card is spotted, a player who plays correctly has a theoretical advantage of up to 13% instead of the normal player disadvantage of around 0.5%. A hole-card player will often choose not to make certain plays, such as hitting a hard 19 against a dealer 20, so as not to reveal that he can see the dealer's hole card.

The strategy can be mitigated by the dealer turning their first card face-up and not dealing their second until the players have all played.

First-basing and spooking

One method of hole carding is to peek at the card when the dealer checks the hole card for blackjack. This is called "first-basing". A modification called "spooking" refers to a partner with a better view peeking at the hole card in the same circumstance and communicating the information to the player. Peeking devices have made these methods largely obsolete.

Front-loading

Front-loading refers to observing the hole card as it is slid under the upcard. Newer methods of hole-carding concentrate on observation before the down card is placed under the upcard. This provides information about the card even if the dealer upcard is not a ten or an ace. The advantage varies depending on the rules, the percentage of cards seen, and the strategies used.