1. An anteriorly concave curvature of the vertebral column; the normal kyphoses of the thoracic and sacral regions are retained portions of the primary curvature (kyphosis) of the vertebral column.
2. A forward (flexion) curvature of the spine; the thoracic spine normally has a mild kyphosis; excessive forward curvature of the thoracic spine may indicate a pathologic condition.
The definition information for kyphosis is provided by Stedman's. You can search our medical dictionary here.