Mardis gras refers to events of the Carnival celebrations, beginning on or after Epiphany and culminating on the day before Ash Wednesday. Mardi gras is French for “Fat Tuesday” (in ethnic English tradition, Shrove Tuesday), referring to the practice of the last night of eating richer, fatty foods before the ritual fasting of the Lenten season, which begins on Ash Wednesday. Related popular practices are associated with celebrations before the fasting and religious obligations associated with the penitential season of Lent. Popular practices include wearing masks and costumes, overturning social conventions, dancing, sports competitions, parades, etc.

Excerpted from Wikipedia.