A blackjack card is simply a standard playing card that is used in the popular casino card game, blackjack. Each card in the deck is assigned a point value, with number cards worth their face value, face cards (Jack, Queen, and King) worth 10 points, and Aces worth either 1 or 11 points, depending on the player's preference.

In blackjack card, players are dealt two cards at the beginning of each hand, and the goal is to have a hand value that is closer to 21 than the dealer's hand, without going over 21. To do this, players must use the cards they are dealt strategically, and decide whether to "hit" (take an additional card), "stand" (keep their current hand), "double down" (double their initial bet and receive one additional card), or "split" (split their hand into two separate hands and play each hand separately).

The point values assigned to each card are critical to the game of blackjack. A player's hand value is calculated by adding up the point values of their cards. For example, if a player is dealt a 7 and a 5, their hand value would be 12. If a player is dealt an Ace and a 9, they have the option of counting the Ace as either 1 or 11, depending on what will give them the better hand value.

The point values of the cards are also important for the dealer, who is required to follow certain rules for hitting or standing. If the dealer's hand value is 16 or less, they must hit until they reach a hand value of 17 or more. If the dealer's hand value exceeds 21, they bust and all remaining players win. If the dealer's hand value is less than or equal to 21, then the player with a hand value closest to 21 without going over wins the round.

In addition to the basic rules of the game, there are also various blackjack strategies that players can use to increase their chances of winning. These strategies involve taking into account the player's hand value, the dealer's up card, and the number of decks being used in the game.

In conclusion, a blackjack card is simply a standard playing card that is used in the popular casino card game, blackjack. Each card is assigned a point value that is used to determine the player's hand value, and to dictate the dealer's actions. The point values of the cards are critical to the game of blackjack, and players must use strategic decision-making in order to achieve a hand value that is closer to 21 than the dealer's hand, without going over 21.