Fat Tuesday, also known as Mardi Gras, gets its name from the practice of consuming rich foods and using up ingredients that may be restricted during the Lenten fasting period that immediately follows the holiday, including butter, oil, sugar and eggs. The term "fat" in this context has both literal and figurative meaning, referring both to the ingredients and quality of traditional foods consumed, which includes fried breads and pastries, and to the figurative quality of fatness being associated with consuming a lot of food in a self-indulgent rather than nourishing way.
The name "Fat Tuesday" also captures the spirit of the event, which is typically marked by general hedonism and unrestrained behavior that, as a religious practice, is a way of preparing for an extended period of restraint lasting from Ash Wednesday in February to Easter Sunday about 47 days later. Mardi Gras is intended as a final push for self enjoyment before the solemnity of the Lenten season that begins with Ash Wednesday the following day. This is why Mardi Gras festivities in some places end immediately at midnight after a day of parties and celebrations on that Tuesday.