Definition of BABINSKI REFLEX. : a reflex movement in which when the sole is tickled the big toe turns upward instead of downward and which is normal in infancy but indicates damage to the central nervous system (as in the pyramidal tracts) later in life —called also Babinski sign, Ba*bin*ski's reflex, \-skēz-\.ADVERTISEMENT. a reflex movement in which when the sole is tickled the great toe turns upward instead of downward and which is normal in infancy but indicates damage to the central nervous system (as in the pyramidal tracts) when occurring later in life—called also Babinski, Babinski sign, Babinski's sign; compare plantar reflex.