Mardi Gras, literally "Fat Tuesday," has grown in popularity in recent years as a raucous event. But its roots lie in the Christian calendar, as the "last hurrah" before Lent begins on Ash Wednesday. That's why the enormous party in New Orleans, for example, ends abruptly at midnight on Tuesday, with battalions of streetsweepers pushing the crowds out of the French Quarter towards home.
What is less known about Mardi Gras is its relation to the Christmas season, through the ordinary-time interlude known in many Catholic cultures as Carnival.
Carnival comes from the Latin words carne vale, meaning "farewell to the flesh." Like many Catholic holidays and seasonal celebrations, it likely has its roots in pre-Christian traditions based on the seasons. Some believe the festival represented the few days added to the lunar calendar to make it coincide with the solar calendar; since these days were outside the calendar, rules and customs were not obeyed. Others see it as a late-winter celebration designed to welcome the coming spring. As early as the middle of the second century, the Romans observed a Fast of 40 Days, which was preceded by a brief season of feasting, costumes and merrymaking, "Fat Tuesday."
Mardi Gras literally means "Fat Tuesday" in French. The name comes from the tradition of slaughtering and feasting upon a fattened calf on the last day of Carnival. Before people would give meat up and fast through Lent.