bursa

A sac containing synovial fluid (a natural lubricant). The purpose is to pad or cushion and thus facilitate motion between soft tissue and bone. Most commonly occurring where tendons pass over bones. bursitis,Inflammation in a bursa that results in swelling due to accumulation of synovial fluid. Capped elbow is inflammation of the bursa over the point of elbow (olecranon process of the ulna). "Capped hock" is inflammation of the bursa over the point of the hock (tuber calcis).