Okay kiddo, do you know what a calendar is? It is a way for us to keep track of time, like the days, weeks, months, and years.
Now, the French Revolutionary Calendar was created by the people of France during the French Revolution more than 200 years ago. They wanted to change things up from the old way of counting time because they wanted to break away from the old order of things.
This new calendar had a new way of naming the days and months. Instead of a week having 7 days, this new calendar had 10-day weeks called "decades".
Also, instead of the usual 12 months, they had 12 new months and each month had 30 days. A year was made up of 365 days, just like our normal calendar.
But here is where it gets a bit tricky. Because a year was actually 365 days and a quarter day, they added 5 extra days at the end of the year and called it "The Sansculottides" (which means "days without breeches"). These days were like a small vacation before the start of a new year.
The French Revolutionary Calendar was in use from 1793 to 1805 until Napoleon Bonaparte came into power and switched back to the old calendar. But some people still use it today for fun or to celebrate certain events.