All around the world there are celebrations going on to mark the last few days before the start of Lent. Shrove Tuesday, or Mardi Gras (literally 'Fat Tuesday') is the last day before the start of Lent, which runs for 46 days until Easter Day.
Traditionally, Christians stopped eating meat and other fatty foods throughout Lent and therefore had to use up all of these things the day before Lent began. Sometimes they shared their food with their friends and neighbours, and when this happened year after year, they turned into parties!
In Venice, Italy there is a huge 12-day-long party where people wear amazing masks. Brazil has the most famous Carnival which lasts for 6 days of dancing and fun.
The word Carnival comes from carnelevare which means "to remove meat".
In a lot of English-speaking countries people eat pancakes on Shrove Tuesday, so they call it Pancake Day!
So Happy Shrove Tuesday, Pancake Day, Mardi Gras and Carnival to everyone! 
