Today is Fat Tuesday. It refers to events of the Carnival celebrations, beginning on or after the Christian feasts of the Epiphany (Three Kings Day) and culminating on the day before Ash Wednesday. Mardi Gras is French for “Fat Tuesday”, reflecting the practice of the last night of eating richer, fatty foods before the ritual fasting of the Lenten season.
Louisiana is the only state in the United States, where Mardi Gras is officially celebrated as a holiday. Celebrations are concentrated for about two weeks before and through Fat Tuesday, the day before Ash Wednesday. Usually, there is one major parade each day (weather permitting); many days have several large parades. The largest and most elaborate parades take place during the last five days of the Mardi Gras season. In the final week, many events occur throughout New Orleans and surrounding communities, including parades and balls (some of them masquerade balls).
In Germany, we celebrate it as Carnival/Fasching. It depends on the region. Around Cologne, it’s called Karneval. In places like Franconia (the northern region of the state Bavaria), they call it Fasching. The celebration on the same day in Germany knows many different terms, such as Schmutziger Donnerstag or Fetter Donnerstag (Fat Thursday), Unsinniger Donnerstag, Weiberfastnacht, Greesentag, and others, and are often only one part of the whole carnival events during one or even two weeks before Ash Wednesday. In German, schmutzig means “dirty”, but in the Alemannic dialects schmotzig means “lard” (Schmalz), or “fat”; “Greasy Thursday”, as remaining winter stores of lard and butter used to be consumed at that time, before the fasting began. Fastnacht means “Eve of the Fast”, but all three terms cover the whole carnival season. The traditional start of the carnival season is on November 11 at 11:11 am (11/11 11:11).
Here is the link to where the Carnival is celebrated all over the world. https://en.wikipedia.org/wiki/Mardi_Gras