A term used to refer to distention of a tendon sheath or joint cavity. It is usually due to a synovial effusion (increased filling of the sheath or joint with synovial fluid) that is caused by a low grade inflammation of the membrane lining of the tendon sheath (synovitis). In most cases the swelling is soft and the horse does not exhibit lameness. If the inflammation is more severe, the distention is more prominent and lameness may be present. The typical location of windgalls is the tendon sheath of the digital flexor tendons or the fetlock joint.