April Fools Day, also called All Fools Day, is first day of April. It was named from the custom of playing practical jokes or sending friends on fools' errands on that date. Although it has been observed for centuries in several countries, the origin of the custom is unknown.

It resembles other festivals, such as the Hilaria of ancient Rome (March 25) and the Holi festival of India (ending March 31). Its timing seems related  to the vernal equinox (March 21),  when nature "fools" mankind with sudden  changes in the weather. On April Fools Day all people are given an excuse  to play the fool.

In France the fooled person is called "Poisson d'Avril" ("April fish"), but the origin of the name is unknown. Though April 1 appears to have been anciently observed in Great Britain as a general festival, it was apparently not until the beginning of the 18th century that the making of April fools was a common custom. In Scotland the custom was known as "hunting the gowk" ("hunting the cuckoo") and April fools were "April gowks," the cuckoo being a term of derision.

The custom of playing April Fools jokes was taken to America by the British. It has continued to be observed by children and adults and sometimes involves rather elaborate hoaxes as well as merely simple jokes.