a congenital defect or opening in the spinal column through which the spinal membranes or spinal cord may protrude, often resulting in hydrocephalus, paralysis, etc.
See spina bifida in American Heritage Dictionary 4
(spīˌnə bĭfˈĭ-də)
noun
A congenital defect in which the spinal column is imperfectly closed so that part of the meninges or spinal cord protrudes, often resulting in hydrocephalus and other neurological disorders. Also called schistorrhachis.