The small of the back is called the small of the back because it's smaller and narrower than the rest of it.
The small of the back is the lower part of the back that is smaller and narrower than the rest.
The small of the back is also the lumbar region of the back.
The human back, also called the dorsum, is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck.
It is the surface of the body opposite from the chest and the abdomen.
The vertebral column runs the length of the back and creates a central area of recession.
The breadth of the back is created by the shoulders at the top and the pelvis at the bottom.
The central feature of the human back is the vertebral column, specifically the length from the top of the thoracic vertebrae to the bottom of the lumbar vertebrae, which houses the spinal cord in its spinal canal, and which generally has some curvature that gives shape to the back.
The ribcage extends from the spine at the top of the back (with the top of the ribcage corresponding to the T1 vertebra), more than halfway down the length of the back, leaving an area with less protection between the bottom of the ribcage and the hips.
The width of the back at the top is defined by the scapula, the broad, flat bones of the shoulders.
The fifth lumbar spine vertebrae (L5) is part of the greater lumbar region.
To the human eye, this is the curve just above the buttocks, which is also commonly referred to as the small of the back.