Osteoarthritis [1] (also called facet joint osteoarthritis or spinal arthritis) occurs when the cartilage that line the facet joints in the spine deteriorate, allowing the bones to rub directly against each other.
With osteoarthritis, bone spurs [2] typically develop over time on the facet joints and may cause pain by pressing on a nerve.
Links:
[1] http://www.spine-health.com/conditions/arthritis
[2] http://www.spine-health.com/conditions/back-pain/bone-spurs-osteophytes-and-back-pain