What is Fat Tuesday?
Fat Tuesday, Shrove Tuesday, Pancake Tuesday, Mardi Gras, Fettisdagen - they are all the same day recognizing the 40 days of fasting preceding Easter known as Lent. (Easter is 47 days after Shrove Tuesday; Lent lasts the first 40 leading to Palm Sunday.)
During Lent, which begins on Ash Wednesday following Shrove Tuesday, many Christian denominations sacrifice foods that give pleasure and take time to reflect on the absolution and confession of sins. Rich or luxurious foods such as meats, sugar, dairy, and eggs are frequently the foods abstained from during Lent, so the day(s) before the Lenten fast are used as a way to consume those foods hanging around the pantry - basically fattening up before the fast and eating as many 'forbidden' foods as possible.
Eating. Drinking. Sharing.