What is the definition or description of: spondylolisthesis?

Spine: Slippage of one vertebral body over another either forwards or backwards.

Spondylolisthesis: is the subluxation or slippage of one vertebral body over another, usually with the more superior body slipping forward relative to the body below. This can be due to to etiologies such as ligamentous laxity or an abnormality of the bone(spondylolysis). If mild, it may be asymptomatic. If severe or unstable, it could cause kinking/compression of the spinal cord or nerve root compression.