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 with international tournaments being held, but most are folk games whose rules may vary by region, culture, location or from circle to circle.
Traditional card games are played with a deck or pack of playing cards which are identical in size and shape. Each card has two sides, the face and the back. Normally the backs of the cards are indistinguishable. The faces of the cards may all be unique, or there can be duplicates. The composition of a deck is known to each player. In some cases several decks are shuffled together to form a single pack or shoe. Modern card games usually have bespoke decks, often with a vast amount of cards, and can include number or action cards. This type of game is generally regarded as part of the board game hobby.
Games using playing cards exploit the fact that cards are individually identifiable from one side only, so that each player knows only the cards they hold 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.
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 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.
Types
Trick-taking games
There are two main types of trick-taking game which have different objectives. Both are based on the play of multiple tricks, in each of which each player plays a single card from their hand, and based on the values of played cards one player wins or "takes" the trick.
Plain-trick games. Many common Anglo-American games fall into this category. The usual objective is to take the most tricks, but variations taking all tricks, making as few tricks (or penalty cards) as possible or taking an exact number of tricks. Bridge, Whist and Spades are popular examples. Hearts, Black Lady and Black Maria are examples of reverse games in which the aim is to avoid certain cards.
Point-trick games. These are all European or of European origin. Individual cards have specific point values and the objective is usually to amass the majority of points by taking tricks, especially those with higher value cards. The main group is the Ace-Ten family which includes many national games such as German Skat, French Belote, Dutch Klaberjass, Austrian Schnapsen, Spanish Tute, Swiss Jass, Portuguese Sueca, Italian Briscola and Czech Mariáš. Pinochle is an American example of French or Swiss origin. All Tarot card games are of the point-trick variety including German Cego, Austrian Tarock, French Tarot and Italian Minchiate.
Matching games
The object of a matching (or sometimes "melding") game is to acquire particular groups of matching cards before an opponent can do so. In Rummy, this is done through drawing and discarding, and the groups are called melds. Mahjong is a very similar game played with tiles instead of cards. Non-Rummy examples of match-type games generally fall into the "fishing" genre and include the children's games Go Fish and Old Maid.
Shedding games
In a shedding game, players start with a hand of cards, and the object of the game is to be the first player to discard all cards from one's hand. Common shedding games include Crazy Eights (commercialized by Mattel as Uno) and Daihinmin. Some matching-type games are also shedding-type games; some variants of Rummy such as Paskahousu, Phase 10, Rummikub, the bluffing game I Doubt It, and the children's games Musta Maija and Old Maid, fall into both categories.
Catch and collect games
The object of an accumulating game is to acquire all cards in the deck. Examples include most War type games, and games involving slapping a discard pile such as Slapjack. Egyptian Ratscrew has both of these features.