Small of the back
The small of the back is at the lower end of the back, above the buttocks. It is at the lumbar curve (where the spine curves inwards), between the waistline and the sacrum. Two prominent structures in that back area are the sacral triangle and the Rhombus of Michaelis.
Lower back pain originates in this area of the lumbar vertebrae. If the spine is curved in deeper than normal, it is called Lordosis. There is also a sexual response in mammals (such as mice, rats, or cats) called Lordosis behavior in which such a posture is assumed to encourage sexual attention and to aid in copulation.
The small of the back in spanking