Internal Medicine Definition
According American College of Physicians:
General Internal Medicine
Many internists enter into practice following completion of their basic internal medicine training. These physicians practice “general internal medicine” and are commonly referred to as “general internists.”
General internists are equipped to handle the broad and comprehensive spectrum of illnesses that affect adults, and are recognized as experts in diagnosis, in treatment of chronic illness, and in health promotion and disease prevention—they are not limited to one type of medical problem or organ system.
General internists are equipped to deal with whatever problem a patient brings—no matter how common or rare, or how simple or complex. They are specially trained to solve puzzling diagnostic problems and can handle severe chronic illnesses and situations where several different illnesses may strike at the same time.
General internists may practice in a variety of settings.
Their training uniquely qualifies them to practice primary care and follow patients over the duration of their adult lives and establish long and rewarding personal relationships with their patients. Although internists may act as primary care physicians, they are not "general practitioners," or "family physicians," whose training is not solely concentrated on adults and may include pediatrics, obstetrics, and surgery.
Some general internists may focus their practice on caring for patients in the hospital setting, and may be referred to as “hospitalists;” the majority of hospitalists in the US are general internists. Still other general internists will combine these facets of care and provide both outpatient and inpatient care for their patients.
Internal medicine physicians are specialists who apply scientific knowledge and clinical expertise to the diagnosis, treatment, and compassionate care of adults providing complete care of their illnesses.
What's an "Internist"?
An Internist must complete at least three of their seven or more years of medical school, and postgraduate training are dedicated to learning how to prevent, diagnose, and treat diseases that affect adults.
Their training qualifies them to practice internal medicine, and you may see these physicians referred to by several terms, including "internists" or "doctors of internal medicine."
Because of their training, their patients, but also they are referred to as the "doctor's doctor," because they are often called upon to act as consultants to assist other physicians to resolve diagnostic problems.