The colorful cake traditionally eaten during Mardi Gras in New Orleans is king cake.
King cake is a ring-shaped pastry associated with Epiphany, the Christian feast commemorating the visit of the Magi, and with the Carnival season leading up to Mardi Gras. In Louisiana, the tradition became especially prominent in New Orleans, where bakeries sell king cakes from January 6 through Fat Tuesday and sometimes throughout the year.
A New Orleans king cake is often made from braided, brioche-like dough and decorated with purple, green, and gold sugar or icing. Those colors are traditionally associated with justice, faith, and power. Modern versions may contain cinnamon, cream cheese, praline, fruit, or other fillings, but the cake itself remains the canonical answer.
A small plastic baby, representing the infant Jesus, is traditionally hidden inside or supplied with the cake. Finding it is considered lucky and may bring responsibility for buying the next cake or hosting the next celebration. King cake is not the same as fruitcake, pound cake, or queen cake; those are separate baked goods.