Onam is Kerala's harvest festival celebrated in honor of the legendary King Mahabali. The festival commemorates the mythical return of Mahabali, who is believed to visit his subjects annually during Onam. It is not a new year celebration (that's Vishu in Kerala), temple festival, or boat race festival (those are separate like Nehru Trophy Boat Race). The legend of Mahabali is central to Onam's significance.