Perhaps because it is complex to explain treatment of diseases that are not localised to a single-organ, there has been confusion about the meaning of internal medicine and the role of an "internist."[16] Internists are qualified physicians with postgraduate training in internal medicine and should not be confused with "interns",[17] who are doctors in their first year of residency training (officially the term intern is no longer in use).[18][19] Although internists may act as primary care physicians, they are not "family physicians," "family practitioners," or "general practitioners," whose training is not solely concentrated on adults and may include surgery, obstetrics, and pediatrics. The American College of Physicians defines internists as "physicians who specialize in the prevention, detection and treatment of illnesses in adults".[20]