The same phrase covers two different things. In blackjack the dealer shows one card, the upcard, and keeps one face down: the hole card. In Texas hold'em the two cards dealt to each player are their hole cards, and everything on the table after that is shared.
In blackjack the hole card is why insurance exists. When the upcard is an ace, the dealer offers a side bet on the hole card being a ten. On a six-deck shoe that bet costs 6.80%, because tens are 30.7% of the unseen cards and the bet is paid as if they were a third of them.
Most American tables have the dealer peek at the hole card when the upcard is a ten or an ace, before anyone acts. If it completes a natural the hand ends there, so you never double or split into a blackjack that was already made. European "no hole card" tables deal the dealer's second card only after every player has finished, which is why doubling and splitting against an ace are priced differently there: the extra money can be lost to a natural that a peeking dealer would have shown first.
In hold'em the two hole cards are the only private information in the hand, and the arithmetic of ranges starts from them: 52 choose 2 is 1,326 combinations, collapsing to 169 hands that play differently. You may use both, one or neither of them at showdown. The best five cards from your two plus the board win, and a hand that uses no hole card at all is playing the board.
Where the numbers come from
Related terms in casino floor
- Upcard, The dealer's one face-up card. It is the only thing you know about the dealer's hand, and it moves the dealer's bust chance from 16.65% to 42.32%.
- Natural, A hand that wins immediately on the first cards dealt.
- Insurance, The side bet offered when the dealer shows an ace. Every source calls it a bad bet; this one gives the figure, and it changes with the number of decks.
- Even money, A 1:1 payout taken on a natural against a dealer ace instead of waiting for 3:2. On six decks it gives up 3.88% of the bet: insurance under another name.
Where an entry quotes a number, that figure comes from the computed sections of this site rather than from another glossary, so the definition and the derivation cannot drift apart. Each entry links to the page where the number is worked out.