This is the curve. Of the spine seen. From the side in terms of the natural sway of the lower back as well as in the neck. It is in the opposite direction of the roundness or kyphosis of the chest region or thoracic spine with the head balanced over the hips with these curves compensating each other to allow this perfect balancing act.
Curvature. Lordosis is the normal anterior curvature of the spine at the level of the waist.
Normal curve. This is the normal, natural curve of the lower spine.