April Fools' Day or All Fools' Day, although not a holiday in its own right, is a notable 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, familiy members, enemies, and neighbours, or sending them on fool´s errand, the aim of which is to embarrass the gullible. Traditionally, in some countries, the jokes only last until noon: like UK, Australia, New Zealand, Canada and South Africa, someone who plays a trick after noon is called an "April Fool". Elsewhere, such as in Ireland, France, and the USA, the jokes last all day.

Source: Wikipedia