Ankylosing Spondylitis is a distinct disease entity characterized by stiffening of a joint, while spondylos means vertebra. Spondylitis refers to inflammation of one or more vertebrae. Ankylosing spondylitis usually is classified as a chronic and progressive form of seronegative arthritis.
Formation of bony bridges between adjacent vertebrae (syndesmophytes) and progressive ossification of extraspinal joint capsules and ligaments are characteristic of the disease.
Spondylitis Association of America – http://www.spondylitis.org/main.aspx