Simplify the following text for a Grade 4 native English-speaking person.
Original: Mardi Gras ( Fat Tuesday ) is a festival held the day before Ash Wednesday , signifying the end of the Carnival season and the start of Lent . Many cities ( especially those with large Catholic populations ) like New Orleans are famous for their Mardi Gras .
Simplified: In some US cities , it is now called `` Mardi Gras Day '' or `` Fat Tuesday '' .