Fat Tuesday refers to the day before Ash Wednesday and the last day of carnival celebration before the Lenten season. The celebrations typically begin on January 6th, on the Christian feast of the Epiphany, and then culminate on Fat Tuesday.
The Lenten season consists of fasting in preparation for Easter. Christians often give up something for Lent as a symbol and offering to Jesus. Mardi Gras is thought of as the time to binge and celebrate before the impending 40-day Lenten season of sacrifice and penance.
Fat Tuesday is sometimes used interchangeably with Mardi Gras, although usually Mardi Gras is considered the carnival preceding Fat Tuesday, according to the Mardi Gras New Orleans website. However, Mardi Gras actually means Fat Tuesday in French.
Mardi Gras celebrations often include Harlequin masks and costumes, drinking, eating, dancing and parades. The holiday has become more secular than its original version, and there are Mardi Gras carnival celebrations all over the United States, including the most popular one in New Orleans. Mardi Gras in New Orleans ends abruptly at midnight, however, with respect to Ash Wednesday.
In the United Kingdom and elsewhere, Fat Tuesday is called Shrove Tuesday. Despite the tradition, there is no mention of Fat Tuesday or Mardi Gras-like celebrations in the Bible.