On the first of April, we celebrate April Fool's Day. The origin of this celebration is uncertain but it seems to have started in France in 1582 when they reformed the calendar under the reign of Charles IX. The Gregorian calendar was introduced and New Year's Day was moved from 25 March-1April (new year's week) to January 1st.
Not everybody knew about this change since communication at that time was not as it is now, almost instant, and they continued celebrating New Year's Day. Those people were known as "fools" and every year they received "fool invitations to non-existent parties" or "fool errands" to ridicule them. People played jokes at them by sticking a paper fish on their backs or things like that.
This tradition spread to England and Scotland on the eighteenth century and then English and French people introduced it to the American colonies, that is why, it is celebrated in many countries nowadays. But if you want to practise your listening skills ...
Click here to find out a bit more about this celebration.
In England, jokes are only played in the morning. It is bad luck to do it after noon. So, be careful in case someone wants to play one at you!