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
See jumping bean in American Heritage Dictionary 4
(jŭmˈpĭng)
noun
A seed, as of certain Mexican plants of the genera Sebastiana and Sapium, containing the larva of the moth Laspeyresia saltitans, whose movements cause the seed to jerk or roll.