When is April Fools' Day?

April Fools' Day or April Fool's Day (rarely called All Fools' Day) is an annual custom in many Western countries on 1 April consisting of practical jokes, hoaxes, and pranks. Jokesters often expose their actions by shouting "April Fool[s]!" at the recipient. Mass media can be involved with these pranks, which may be revealed as such the following day. The custom of setting aside a day for playing harmless pranks upon one's neighbor has been relatively common in the world historically.

From Wikipedia’s article April Fools' Day, by its contributors, under CC BY-SA 4.0.