| Degeneration | A wear and tear phenomena. When the joints of the body wear out, it is referred to as osteoarthritis, also known as degenerative joint disease. |
| Diagnosis | The act of distinguishing one health problem from another. |
| Diagnostic imaging | The use of X-rays, MRI, CAT scans, EMG, thermography and other tools to create pictures of the structure and function of the body. |
| Disability | The partial or total loss of mental or physical abilities caused by an injury or disease that prevents an insured from engaging in some or all of the duties of his or her usual occupation. |
| Disc Herniation | An extreme bulging of the soft nucleus pulposus into a defect or weakened area of fibrous disc exterior. |
| Disc | A cartilage (cushion/pad) that separates each spinal vertebra, absorbs shocks to the spine and protects the nerve systems and assists in creating the four spinal lateral curves. |
| Disease | Any deviation from or interruption of the normal structure or function of any part, organ, or system of the body that is manifested by a characteristic set of symptoms whose prognosis may be known or unknown. |
| Dorsal | Pertaining to the back; the twelve thoracic vertebrae are also referred to as dorsal vertebrae. |