Babinski reflex

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An extension of the great toe, sometimes with fanning of the other toes, in response to stroking of the sole of the foot. It is a normal reflex in infants, but it is usually associated with a disturbance of the pyramidal tract in children and adults.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine An abnormal plantar reflex in which the hallux moves upwards, indicative of motor neuron damage.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun extension upward of the toes when the sole of the foot is stroked firmly on the outer side from the heel to the front; normal in infants under the age of two years but a sign of brain or spinal cord injury in older persons