What is the origin of Fat Tuesday / Mardi Gras?
Mardi Gras, which is French for “Fat Tuesday,” is the last day of a season called “Carnival.” The Carnival season is characterized by merrymaking, feasting, and dancing. Mardi Gras is the culmination of festivities and features parades, masquerades, and, unfortunately, often drunkenness and shameless debauchery. Carnival is typically celebrated in Catholic countries of southern Europe and Latin America.
The excess of Carnival may not seem to have much in common with the austerity of Lent, but the two seasons are inseparable. The day after Fat Tuesday is Ash Wednesday; therefore, the end of Carnival is followed immediately by the beginning of Lent. Lent is a time of fasting and penance in preparation for Easter. Carnival, then, can rightly be seen as the indulgence before the fast. It is one last “binge” before having to give something up for 40 days.
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(Warning: This video does contain some immodestly dressed women but nothing more than what you'd see on PBS.) Carnival is a pagan celebration though it is celebrated by professing Christians (particularly Roman Catholics) worldwide as a "one last hoorah" celebration before the Lenten fast.