Final answer:
The curve in the lower part of the human spine is known as lumbar lordosis, which is the natural concave curve in the lumbar region, contrasting with the upper back's thoracic kyphosis.
Step-by-step explanation:
The curve in the lower part of the human spine is known as lumbar lordosis. This is an excessive anterior curvature of the lumbar region of the vertebral column. Normal lordosis is the naturally occurring, slightly concave curve in the lumbar region, but lordosis can also refer to abnormal or excessive curvature, which is associated with conditions like obesity or late pregnancy. In contrast, lumbar kyphosis, thoracic kyphosis, and thoracic lordosis refer to different regions or types of spinal curvature. Lumbar kyphosis is not a term generally used to describe a normal spine curvature, as the lumbar curve is normally lordotic, not kyphotic. Thoracic kyphosis is the naturally occurring curve in the upper back, and if excessive, it's referred to as kyphosis or 'hunchback.' Thoracic lordosis is not a typical term because the thoracic curve is normally kyphotic.