Final answer:
Kyphosis is the correct term for an abnormal curvature of the posterior thoracic spine. It refers to an excessive posterior curvature of the upper thoracic region of the spine, often resulting in a humpback or hunchback appearance.
Step-by-step explanation:
An abnormal curvature of the posterior thoracic spine is called kyphosis. The vertebral column naturally has three curves: the cervical, thoracic, and lumbar curves. Kyphosis refers to an excessive posterior curvature of the upper thoracic region of the spine. This condition can be caused by factors such as osteoporosis or developmental anomalies, resulting in a humpback or hunchback appearance.