The term "Mardi Gras" is French for "Fat Tuesday." In Spanish it would be Martes Grande. Mardi Gras has been celebrated for hundreds of years in countries throughout the world. The celebration takes place within a few days before today, Fat Tuesday, which is always the Tuesday right before Ash Wednesday.
Ash Wednesday is a holy day in the Catholic Church (and some other religions), the beginning of Lent, 46 days before Easter Sunday. On Ash Wednesday, members of the church go to mass and palm fronds are burned, with the ashes smeared on the foreheads of the church members. Ash Wednesday is the first day of Lent, which is considered a period of repentence. Many Catholics give up something during Lent -- like candy for the children, meat for some adults -- as a sign of repentence for their sins, and sacrifice. Putting ashes on the forehead signifies repentence, a reminder that we will all return to ashes some day.
Remember, O man, that you are dust, and unto dust you shall return. Genesis, 3:19
The days (and sometimes weeks) leading up to Ash Wednesday are celebrated in many countries, and notably in New Orleans, Lousiana, with a city-wide carnival, people dressing up in costumes and partying through the nights, parading through the streets, enjoying their last days of celebration before the 46-day period of Lent.
"Cajun" is a term that is used to refer to a certain group of people in southwest Lousiana. They originally moved from France to Canada, to an area known as Acadia, which included parts of Nova Scotia, Quebec, and Maine. When the English took over, the Cajuns were thrown out in what was called Le Grand Derangement, and many of them moved to Lousiana.
Once in Lousiana, the people of French origin intermarried with all the other groups in the area, and it is the product of those people who are called "Cajun." In that area of Lousiana, many of the people still speak French in their own homes, and observe their own unique culture, which is reflected in their food, language, and music. "Jolie Blon," is a cajun song known and preformed world-wide. It is sometimes called the Cajun National Anthem:
We all know about the parties in New Orleans, with the beads and the costumes. But did you know that in Polish-American communities around the country, today is celebrated by the making and eating of a Polish pastry called paczkis, like a jelly donut dipped in sugar. Ummmm. Happy Mardi Gras. Eat some donuts, they're good for you this one day out of the year. Even if you're not Polish.