Lumbar spinal stenosis: A condition whereby either the spinal canal (central stenosis) or vertebral foramen (foraminal stenosis) becomes narrowed, leading to compression of the spinal nerves. Symptoms are pain in the lower back and weakness, numbness, pain, and loss of sensation in the legs. The most common cause of lumbar spinal stenosis is degenerative arthritis (osteoarthritis), but other causes can include tumor, infection, and various metabolic bone disorders. Treatment may involve anti-inflammatory medications, corticosteroids, medications to treat nerve pain, physical therapy, and in severe cases, surgery. Also referred to as lumbar stenosis, or spinal stenosis. Spinal stenosis frequently responds to exercise.