Temporomandibular Joint Disorder (TMJ), also known as temporomandibular joint dysfunction, refers to a group of conditions that affect the temporomandibular joint (TMJ) and the surrounding muscles. The TMJ is the joint that connects your jawbone to your skull, allowing you to move your jaw up and down and side to side, enabling actions like chewing, speaking, and yawning. TMJ disorder can cause discomfort and pain in the jaw joint and the muscles that control jaw movement.