The term lordosis refers to the normal inward lordotic curvature of the lumbar and cervical regions of the spine. Excessive curvature of the lower back is known as lumbar hyperlordosis, commonly called sway back, hollow back or saddle back (after a similar condition that affects some horses). A major feature of lumbar hyperlordosis is a forward pelvic tilt, resulting in the pelvis resting on top of the thighs. Curvature in the opposite convex direction, in the thoracic and sacral regions is termed kyphotic. When this curvature is excessive it is called kyphosis or hyperkyphosis.