Scoliosis curves are measured and expressed by degree. The higher the degree the more the scoliosis is said to be 'severe'.
The normal thoracolumbar spine is relatively straight in the sagittal plane and has a double curve in the coronal plane. As shown below, the thoracic spine in convex posteriorly (kyphosis) and the lumbar spine is convex anteriorly (lordosis). Normally there should be no lateral curvature of the spine.