A bump on the Buddha's head signifying wisdom; one of the 32 marks of greatness.

One of the thirty-two marks of a great man distinguishing the Buddha. The ushnisha is the bump protruding from the top of his head. Sometimes, it appears as a bun of twisted hair gathered together. In other cases it is perfectly smooth or covered with snail-shell shaped curls. Some interpret this mark as signifying the Buddhaâ€(tm)s extraordinary mental powers.

(Sanskrit) The protuberance at the top of the head of a Buddha Rupa representing the flame of supreme enlightenment.