Source : Webster's Revised Unabridged Dictionary (1913)

Spina bifida \Spi"na bif"i*da\ (Med.) [L., cleft spine.]
   A congenital malformation in which the spinal column is cleft
   at its lower portion, and the membranes of the spinal cord
   project as an elastic swelling from the gap thus formed.

Source : WordNet®

spina bifida
     n : a not uncommon congenital defect in which a vertebra is
         malformed; unless several vertebrae are affected or there
         is myelomeningocele there are few symptoms; can be
         diagnosed by amniocentesis [syn: {rachischisis}, {schistorrhachis}]