Wiktionary
n. A set of four smaller muscles in the shoulder responsible for rotating the humerus (upper arm bone).
WordNet
n. a supporting structure of the shoulder consisting of the muscles and tendons that attach the arm to the shoulder joint and enable the arm to move
Wikipedia
In anatomy, the rotator cuff (sometimes incorrectly called a "rotator cup", "rotor cuff", or "rotary cup") is a group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff are over half of the seven scapulohumeral muscles. The four muscles are the supraspinatus muscle, the infraspinatus muscle, teres minor muscle, and the subscapularis muscle.
Usage examples of "rotator cuff".
It's like, like having last year's Cy Young winner sitting in the bullpen in case one of the starters blows a rotator cuff.
The new arm will settle into the rotator cuff as if it grew there.
There's damage to the rotator cuff and the whole shoulder, as well as to the lower arm itself.
No living person would lie in such an awkward position, face pressed to the drain, his right arm twisted behind his body at a torturous angle that suggested a dislocated shoulder or even a torn rotator cuff.