TMJ is often used as an abbreviation for disorders that affect the temporomandibular joint and the associated muscles that control jaw movement. The temporomandibular joint or jaw joint is situated on either side of your head in front of your ears, where your lower jaw articulates with the skull.

This joint allows you to talk, chew and yawn. Jaw movement is generally smooth without deviations or deflections, and this is achieved by an articular disc or cartilage that is located between the lower jawbone and skull. The TMJ obeys the same orthopaedic principles as other joints such as the knee or ankle. Consequently, one can 'sprain' their TMJ in a similar fashion to spraining your ankle or knee.