Conventional terminology of three-dimensional description of spinal deformity is ambiguous and mostly tied to either a frontal or sagittal plane view of the spine. The article proposes a rationalized system for describing the shape of the spine. The spine is viewed as a line in space ('vertebral body line') with three 'angulations' specifying the orientation of each vertebra. Four axis systems are defined for the whole body, the spine, curve regions, and individual vertebrae, respectively. These in turn define the principal planes of the body, spine, curve regions, and vertebrae. Curvature can be defined as a local measure at a point on the vertebral body line, or as a regional measure between specified end vertebrae. Torsion is defined both as a local geometric property of the vertebral body line, and as measure of the relative axial plane angulations between specified vertebrae. Linear distance measures define the deviations of specified vertebrae from the local, regional, spinal, and global axis systems. Practical recommendations for positioning patients are made. This new system of terminology recognizes the 3-dimensional nature of scoliosis and other spinal deformities and is intended to rationalize communication in both research and clinical practice.