WordNet (r) 3.0 (2006):

Babinski
    n 1: 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 [syn:
         Babinski, Babinski reflex, Babinski sign]