A Doctor of Medicine (abbreviated MD) is a degree awarded by an university, and more specifically, a medical school, that is often a step towards the practice of medicine. That degree sometimes exists as a MBBS as well. It is often considered a major milestone before licensure, as well as a requirement to become chief medical officer on most starships. Holders are addressed as doctors. Unlike most species, the Lyrans considered the MD as the license to practice medicine. (Star Trek: The Stoneship Files: "Educational Armageddon")