This refers to the rotator cuff and bursa being impinged between the humerus (arm bone) and the acromion (part of the shoulder blade) when your arm reaches overhead. 

Non-surgical treatment: analgesia; treatment usually involves physiotherapy; steroid injection into the bursa (sac of lubricating fluid) adjacent to the rotator cuff. 

Surgical treatment: arthroscopic subacromial decompression, which involves shaving some bone off the outer aspect of the acromion (part of the shoulder blade) via keyhole incisions (arthroscopy).

Such surgery is often performed alongside one or more or the following:

• Cuff repair
• Biceps tenotomy / tenodesis
• Lateral clavicle excision