In English, Mardi Gras refer to events of the celebrations, ending on the day before Ash Wednesday. From the French term "Mardi Gras" (literally "Fat Tuesday"), the term has come to mean the whole period of activity related to those events.
What many people don't know is that Mardi Gras varies from city to city, as some traditions consider Mardi Gras as the Carnival period between Epiphany or Twelfth Night and Ash Wednesday. In Mobile, Alabama, another hot-spot for party-goers, Mardi Gras events begin in November, followed by mystic society balls on Thanksgiving, then New Year's Eve, formerly with parades on New Year's Day, followed by parades and balls in January and February, celebrating up to midnight before Ash Wednesday.
So, in reality, it appears Mardi Gras means a period of time to have fun.