What is a king cake and what does it mean to get the baby?

A king cake is a traditional cake served and eaten on Mardi Gras. Typically it is in a round shape, is a plain cake (like angel food, vanilla, or pound cake), and is decorates with a very sweet icing. Often, the decorations and icing colors are done up to match those of Mardi Gras (green, gold, and purple). There is a little toy baby or "king" buried into the cake. Whoever finds the baby is considered to be lucky and is "king" (or queen) for the day.