The group of four muscles that hold the humeral head in place are collectively known as the rotator cuff.  These muscles are assisted in glenohumeral stability by the joint capsule and ligaments.  The rotator cuff muscles (infraspinatus, supraspinatus, teres minor and subscapularis) are part of the glenohumeral joint and they share a common tendon.  It is  this tendonous attachment that covers the humeral head and resembles a cuff.