Short answers, pulled from the story.
A card game is any game that uses cards as the primary device with which the game is played, whether the cards follow a traditional design or are created specifically for the game. Card games are often characterized as games of imperfect information, because each player knows only the cards they hold and not those held by anyone else.
Playing cards were likely invented during the Tang dynasty in China, around the 9th century, helped by the technology of woodblock printing. The oldest surviving reference is from 868, when Princess Tongchang, daughter of Emperor Yizong of Tang, was recorded playing the leaf game with her husband's family.
The earliest dated instance of a game involving cards occurred on the 17th of July 1294, when the Yuan dynasty Department of Punishments caught two gamblers, Yan Sengzhu and Zheng Zhugou, playing with paper cards. The officers impounded the printing wood blocks along with nine of the cards, but recorded no description of the game.
Playing cards first appeared in Europe in the last quarter of the 14th century, with the earliest mention in a Catalan rhyme dictionary in 1371. Early European references speak of a Saracen or Moorish game called naib, and a near-complete Mamluk Egyptian deck of 52 cards survives from around the same time.
The two great innovations are trump cards and bidding. Trump cards, able to beat all cards in other suits, first appeared with tarot as the trionfi, while bidding first emerged in the 17th century in the Spanish game of Ombre.
A small number of card games have formally standardized rules and international tournaments, governed by bodies such as the World Bridge Federation for bridge and the International Skat Players Association for skat. Most card games, however, are folk games whose rules vary by region, culture, location or from circle to circle, with players free to adopt their own house rules.
The card had been called a jack within the terminology of all-fours since the 17th century, but the word was once considered vulgar. The abbreviation Kn for knave was easily confused with the king, so the change to jack took hold after 1864, when Hart reintroduced corner indices along with the knave-to-jack change.