Bursitis of the shoulder is inflammation of the bursa found between the bone at the top of the shoulder (the acromion), the upper arm bone (humerus), and the tendons and muscles.

A bursa is a fluid-filled sac that cushions and lubricates areas of the body where friction is likely to occur. Examples of such areas include between two bones, between a tendon or ligament and a bone, or between bone and skin.