Bursa 

A bursa is a fluid filled sac located between muscle tendons or ligaments and bone that reduces compression pressure and friction between these structures. With over 150 bursae in your body, they help smooth joint movement. Habitually overloading the associated tendons or ligaments can over compress your bursa leading to chronic irritation, swelling and pain - a condition called bursitis. Over time the bursa may even become calcified.