any of several card games in which four points may be scored during the play of a hand, for winning the high trump, low trump, and jack of trumps, and for “game” (the largest high-card count)
See all fours in American Heritage Dictionary 4
plural noun(used with a sing. verb)
Any of several card games resembling whist and in which points are scored in four ways: for the high trump, the low trump, the jack of trumps, and the game.