April Fool's Day
April Fools' Day (sometimes called April Fool's Day or All Fools' Day) is celebrated every year on the first day of April. Popular since the 19th century, the day is not a national holiday in any country, but it is well known in Canada, Europe, Australia, Brazil and the United States, and it is celebrated as a day when people play practical jokes and hoaxes on each other. The jokes and their victims are known as ""April fools"". Hoax stories may be reported by the press and other media on this day and explained on subsequent days.
In the Middle Ages, New Year's Day was celebrated on Lady Day, the Feast of the Annunciation on 25 March, in most of Europe. The feast's octave was 1 April. The holiday may have originated in France as part of the shift to celebrating New Year's on 1 January, a move formalized as part of the 1564 Edict of Roussillon. It may have appeared earlier in Chaucer, but this is now generally discounted.
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All details taken directly from provider content at http://en.wikipedia.org/wiki/April_Fools'_Day