Your Temporomandibular joint is a hinge that connects your jaw to the temporal bones of your skull, which are in front of each ear. It lets you move your jaw up and down and side to side, so you can talk, chew, and yawn. Inside the jaw joint, there is a smooth material called cartilage, covering part of the bones. There is also a cartilage disc within the joint. The joint is lubricated by fluid called synovial fluid.
Problems with your jaw, the muscles in your face that control the joint, as well as internal components of the joint, are collectively known as temporomandibular disorders (TMD). But you may hear it wrongly called TMJ, after the joint.