Lordosis - commonly referred to as swayback or hyper-lordosis

Lordosis (commonly referred to as swayback or hyper-lordosis) is a medical term used to describe an inward curvature of a portion of the vertebral column. Two segments of the vertebral column, namely cervical and lumbar, are normally lordotic, that is, they are set in a curve that has its convexity in front and concavity behind, in the context of human anatomy. When referring to the anatomy of other mammals, the direction of the curve is termed ventral. Curvature in the opposite direction, that is, apex posteriorly (humans) or dorsally (mammals) is termed kyphosis.

Lordotic curvatures of the vertebral column, also known as secondary curvatures are caused mainly because of the difference of thickness between the anterior and posterior part of the intervertebral disc. Those curvatures start to appear during the fetal period, but don't become evident until lactation.

Excessive lordotic curvature is also called hollow back, saddle back, and swayback. Loss of lordosis is sometimes seen with painful spinal conditions. If rigid, usually after spinal fusion surgery, it is known as flat-back.

The familiar concave shape of the horse's back is, by extension, described as lordotic.

Lordosis also refers to the position that some mammals (cats, mice, rats etc) display when they are ready to mate. The position receives its name from the way the spine curves when the animal is in this position.