April 1, celebrated in various countries, including the United States and Great Britain, and marked by the playing of practical jokes. Also called All Fools' Day. All 'Fools' Day April 1st, a day when people play tricks on each other. or All Fools' Day First day of April, named for the custom of playing practical jokes on that date. Though it has been observed for centuries in several countries, including France and Britain, its origin is unknown. It resembles the Hilaria festival of ancient Rome (March 25) and the Holi festival of India (ending March 31). The custom of playing April Fools' jokes was brought to America by the British