Congenital condition where the spine doesn't form properly and vertebrae remain open. The spinal cord also doesn't form properly.
This often results in congenital paralysis.
There is also a type of spina bifida, called occulta, where there is no major deformity, but there is a slight malformation of the vertebrae, causing little to no problem, and often going unnoticed unless there are X-Ray taken. There have been conjectures that people who's BIID focuses on paraplegia may have spina bifida occulta. This could only be proven by systematic study and X-Ray of these individuals