Fibromyalgia: A syndrome characterized by chronic pain, stiffness, and tenderness of muscles, tendons, and joints without detectable inflammation. Fibromyalgia does not cause body damage or deformity. However, undue fatigue plagues the large majority of patients with fibromyalgia and sleep disorders are common in fibromyalgia.

Fibromyalgia is considered an arthritis-related condition. However,it is not a form of arthritis (a disease of the joints) since it does not cause inflammation in the joints, muscles, or other tissues or damage them. But fibromyalgia can (like arthritis) cause significant pain and fatigue and it can similarly interfere with a person's ability to carry on daily activities.