April 1st is an unofficial holiday in the United States called April Fool's day. In the past, April 1st used to be celebrated as the New Year. And then in the year, I think, 1592, or something like that, the official New Year was changed to January 1st and some people never heard of this change so they continued to celebrate the New Year on the April 1st, but the people who knew of this change called them fools. A fool in English

is someone who is not smart. We have many words for this in English: dumb, a dummy, stupid, imbecile, idiot, but you're all nice people so you'll never need to use those words so you can forget that. But the people who continued to celebrate the New Year's on April 1st were called April fools. So a tradition started, that on April 1st people would try to make, would do pranks on other people.