These intervertebral discs are shock absorbers or cushions between the vertebral body. With time these discs degenerated and dry. This could lead to compression of the nerve roots loading of the joints, which cause pain.
Radiculopathy is when the nerve roots are irritated and can cause pain throughout the body. In the neck or cervical spine, this can cause neck pain but, more commonly, arm pain. In the thoracic spine, this can cause rib pain or back pain. In the lumbar spine, this can cause leg pain buttocks pain or back pain. This pain can occur due to nerve compression from the degeneration of surrounding structures or chemical irritation primarily from the disc. This can be treated with epidural steroid injections.
Facet/zygapophyseal arthropathy are small joints that can get irritated. This is due to overuse trauma or rheumatological conditions. These joints are located between the adjacent vertebral bodies and can be treated with thoracic facet injections and rhizotomies.
Its most general description merely means narrowing of the spinal canal. It can occur at any level of the spine, whether it be the cervical thoracic or lumbar regions. There is central stenosis where typically the spinal nerve roots or spinal cord lies. There is lateral recess and neuroforaminal stenosis which, all could involve the individual nerve roots.