Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek: παραπληγίη "half-striking". It is usually caused by spinal cord injury or a congenital condition such as spina bifida that affects the neural elements of the spinal canal. The area of the spinal canal that is affected in paraplegia is either the thoracic, lumbar, or sacral regions. If all four limbs are affected by paralysis, quadriplegia is the proper terminology. If only one limb is affected, the correct term is monoplegia.

Spastic paraplegia is a form of paraplegia defined by spasticity of the affected muscles, rather than flaccid paralysis.