All fours is a traditional English card game, once popular in pubs and taverns as well as among the gentry, that flourished as a gambling game until the end of the 19th century. It is a trick-taking card game that was originally designed for two players, but developed variants for more players. According to Charles Cotton, the game originated in Kent, but spread to the whole of England and eventually abroad. It is the eponymous and earliest recorded game of a family that flourished most in 19th century North America and whose progeny include pitch, pedro and cinch, games that even competed with poker and euchre. Nowadays the original game is especially popular in Trinidad and Tobago, but regional variants have also survived in England. The game's "great mark of distinction" is that it gave the name 'jack' to the card previously known as the knave.

A Jack or Knave, in some games referred to as a Bower, in Tarot card games as a Valet, is a playing card which, in traditional French and English decks, pictures a man in the traditional or historic aristocratic or courtier dress, generally associated with Europe of the 16th or 17th century. The usual rank of a jack is between the ten and the queen.