Your shoulder has three bones: the scapula (shoulder blade), humerus (upper arm bone), and clavicle (collarbone). They work together in a ball-and-socket joint where the arm connects to your trunk.
Your shoulder’s labrum is soft tissue that helps connect the socket part of the scapula (called the glenoid) with the head of the humerus. If the labrum tears, there’s not enough cushion between those bones. You also have a labrum in your hip sockets, which also acts like a connective cushion.