A card game is any game using playing cards as the primary device with which the game is played, be they traditional or game-specific.
Countless card games exist, including families of related games (such as poker).
A small number of card games played with traditional decks have formally standardized rules, but most are folk games whose rules vary by region, culture, and person.
Games using playing cards exploit the fact that cards are individually identifiable from one side only, so that each player knows only the cards he holds and not those held by anyone else.
For this reason card games are often characterized as games of chance or “imperfect information”—as distinct from games of strategy or “perfect information,” where the current position is fully visible to all players throughout the game.
Many games that are not generally placed in the family of card games do in fact use cards for some aspect of their gameplay.
Similarly, some games that are placed in the card game genre involve a board.
The distinction is that the gameplay of a card game chiefly depends on the use of the cards by players (the board is simply a guide for scorekeeping or for card placement), while board games (the principal non-card game genre to use cards) generally focus on the players' positions on the board, and use the cards for some secondary purpose.
A card game is played with a deck or pack of playing cards which are identical in size and shape. Normally the backs of the cards are indistinguishable.
The faces of the cards may all be unique, or there can be duplicates. In some cases several decks are shuffled together to form a single pack or shoe.
The first playing cards appeared in the 9th century during Tang-dynasty China.
The first reference to the card game in world history dates no later than the 9th century, when the Collection of Miscellanea at Duyang, written by Tang Dynasty writer Su E, described Princess Tongchang (daughter of Emperor Yizong of Tang) playing the "leaf game" with members of the Wei clan (the family of the princess' husband) in 868 .