Doctors are people who have trained themselves in techniques to heal either humans or animals. While people who treat humans are called doctors and the ones who treat animals are called veterinary doctors. In the case of humans there are various specialties and super-specialties. For instance cardiology, Hepatology, Neuro surgery etc. They commonly get an MBBS (Bachelor of Medicine and Bachelor of Surgery) degree after which they attain and MD. There are other types of specialties that do not deal with allopathic medication and is known as Alternative medicine. People practicing those specialties are also known as doctors.