What is temporomandibular joint disorder?

Inflammation: Temporomandicular joint disorder (TMJ) is a common inflammatory condition of the joint between your jaw bone and your skull at the temples. This joint is subject to trauma, overuse, arthritis, etc. Just like any other joint. If you suspect this condition, see your family doctor or internist for treatment options and a possible referral.

Wikipedia: Wikipedia says it well: an umbrella term covering acute or chronic pain, especially in the muscles of mastication and/or inflammation of the temporomandibular joint, which connects the mandible to the skull. Can be on its own or can be associated with conditions like rheumatoid arthritis.

TMD: TMD are disorders of the jaw joint - TMJ. Can involve the bone, disk, ligaments. Most common TMD is disc displacement. Triad of symptoms - joint pain, limited oral opening and joint noises.