Fat Tuesday is the day before Ash Wednesday (the beginning of Lent). Not eating meat during Lent is a tradition that goes back to the medieval days (within the Catholic church). Since there weren't any refrigerators, freezers, etc....rather than let the food spoil, they would have a huge party eating all the meat before it spoiled with the Tuesday before....being the last day and the term Fat Tuesday. Today, practicing Catholics are expected to observe the no meat eating on Fridays instead of the entire Lent season which is why you see McDonalds advertising $1 Filet-O-Fish, Fish Frys, etc. Seafood isn't considered meat by Catholic standards. I presume the pancake tradition also fits into the no meat observance rather than bacon and eggs. Since New Orleans was part of a French Colony and Catholicism the prevalent religion, that is why there is Mardi Gras which literally translates into "Fat Tuesday".
"The farther we go, the more the ultimate explanation recedes from us, and all we have left is faith."