The term lordosis refers to the abnormal inward curvature of the lumbar and cervical regions of the spine. Excessive or hyperlordosis can happen and lumbar hyperlordosis is commonly referred to as sway back, hollow back or saddle back, a term that originates from the similar condition that arises in some horses. A major factor of lordosis is forward pelvic tilt, when the pelvis tips forward when resting on top of the thighs. Curvature in the opposite direction is termed kyphosis.