Mardi Gras doesn't mean "goodbye meat". Carnivale does. Shrove Tuesday is something different again.
Lundi — Monday
Mardis — Tuesday
Mercredi — Wednesday
Jeudi — Thursday
Vendredi — Friday
Samedi — Saturday
Dimanche — Sunday
Gras - fatty, greasy; fat (noun) - as in the stuff inside sausages, etc.
Foie = liver, e.g. cirrhose du foie = cirrhosis of the liver, huile de foie de morue = cod-liver oil
Pate = paste (noun, e.g. pate a bois = wood filler) or mixture
pate de foie gras = mashed-up paste made from fatty liver
Mardis gras = greasy/fatty Tuesday
carne = meat or flesh (carnal desires, chile con carne = chile with meat)
vale = farewell (usually seen in eulogies, funeral orations as "Vale [whatsisname]"
This is usually anglicised as just 'carnival', and has come to mean things related to the time of 'misrule', celebration & so forth that happened before the start of Lent.
I guess in Europe that would have been at the miserable fag-end of winter, just when it was starting to turn so you could see spring on the way. I've heard a few Europeans say that February was the worst month usually, so a bit of a break-out could be a good idea - something to look forward to, something to work the last demons of darkness out of the spirit before you settle down for the haul to Easter.
Note, 'shrove' is like 'shrive', as in 'short shrift' - that is, absolution after confession . Because you'd be shriven before attending the very serious Ash Wednesday mass for the beginning of Lent. Maybe you'd do it at the end of the day, after letting loose earlier.