The rotator cuff is a group of four tendons that attach to muscles that control the movement of the shoulder joint. The rotator cuff itself stabilizes the joint. A rotator cuff injury may be due to a sudden (acute) event or from gradual damage that builds up over time. Shoulder pain is the primary symptom of rotator cuff injury.

https://www.medicinenet.com/rotator_cuff_injury_symptoms_and_signs/symptoms.htm