Mardi Gras was a carnival which took place in New Orleans. Carnival-goers would wear masks and costumes.
Rose Tyler was disappointed that, when the Tenth Doctor told her he had a brilliant idea, he meant stamp collecting, not something fun like going to Mardi Gras or visiting a planet where everything was made out of ice cream. (PROSE: Stamp of Approval)
Behind the scenes Edit
In the real world, Mardi Gras is celebrated on the same day as Shrove Tuesday.