either of a pair of nerves, the largest in the body, that originate in the sacral plexus of the lower back and extend down the buttocks to the back of the knees, where they divide into other nerves: the sciatic nerve and its branches innervate large areas of the pelvis, leg, and foot.
a nerve network originating from the nerves of the sacral spine and innervating large areas of the lower trunk and legs, especially via the sciatic nerves.
