A Doctor of Medicine, abbreviated MD, was a degree and a title awarded to a student at a medical college. An individual who earned an MD could be a physician, a surgeon, or both. Originally from pre-FederationEarth, this degree was assimilated into the Federation educational system in the 22nd century.
Medical careers in Starfleet varied depending upon specialties. In order to be a chief medical officer, a physician was required to be highly skilled in both surgery as well as in general medicine. (citation needed • edit)