April Fools' Day or All Fools' Day is a day celebrated in many countries on April 1. The day is marked by the commission of hoaxes and other practical jokes of varying sophistication on friends, family members, enemies, and neighbors, or sending them on a fool's errand, the aim of which is to embarrass the gullible. Traditionally, in some countries, such as the UK, Australia and South Africa the jokes only last until noon, and someone who plays a trick after noon is called an "April Fool". Elsewhere, such as in Canada, France, Ireland, Italy, Russia, The Netherlands, and the U.S., the jokes last all day.
The origin of April Fools' Day is obscure. One likely theory is that the modern holiday was first celebrated soon after the adoption of the Gregorian calendar; the term referred to someone still adhering to the Julian Calendar, which it replaced. In many pre-Christian cultures May Day (May 1) was celebrated as the first day of summer, and signalled the start of the spring planting season. An April Fool may have been someone who did this prematurely. Another possible origin lies in the fact that when King Charles IX of France officially changed the first day of the year from April 1 to January 1, some of his subjects continued using the old system.
In the eighteenth century the festival was often posited as going back to the time of Noah. According to an English newspaper article published April 13, 1789, the day had its origin when Noah sent his dove off too early, before the waters had receded; he did this on the first day of the Hebrew month that corresponds with April. A possible reference to April Fools' Day can be seen in the Canterbury Tales (ca 1400) in the Nun's Priest's tale, a tale of two fools (Chanticleer and the fox), which took place on March 32. (From: Wikipedia, license: CCA-SA)