April Fool's day is a custom of playing practical jokes on each other. The origin of this custom is uncertain but there are many legends surround this event. Aside from Christian disputes over Julian to Gregorian calender that resulted in April fool's day, there are also myths about Muslims being fooled into massacre by the Christians on this day. Yet the other is that earth’s indigenous people celebrating the arrival of the spring and playing pranks over each other to enjoy the festival. Nothing is concrete, but on this day people are given excuse to play fool by means of deception, tell lies, create fear in others, etc. to create some fun. Some moralists, including in Islam, take the position that merriments if an outcome of lies and deception is not principally sound.
But whatever they may be, one thing is sure. There are more fools in the month of April than in any other months of the year.