Real Dictionary

jumping bean in American English
the seed of any of several Mexican plants (esp. genus Sebastiana) of the spurge family, containing the larvae of a small moth (Cydia saltitans), which by its movements makes the seed jump or roll about
noun: the seed of any of certain Mexican plants of the genera Sebastiania and Sapium, of the spurge family: the movements of a moth larva inside the seed cause it to move about or jump

jumping bean in British English
noun: a seed of any of several Mexican euphorbiaceous plants, esp species of Sebastiania, that contains a moth caterpillar whose movements cause it to jerk about