An internist is a doctor of internal medicine: the organs inside you — heart, lungs, stomach, liver, and so on — and the illnesses that are treated with medicine, not with a knife. They have a wide view of the whole inside of the body. For a messy, unclear problem that is “inside”, they are often the person you see first among specialists, and they may send you on to a narrower doctor if needed. They do not do operations; that is the surgeon’s work. This is especially US English. In Britain people more often say physician for this kind of doctor, and internist is much less common. In a Taiwan hospital you are looking for 內科. Though actually, the name looks like intern, and that tricks learners every year. An intern is a junior doctor still in training (or a trainee in any job). An internist is already the specialist. The intern- here is the “internal” intern- — inside the body — from German Internist, not the trainee intern.

內科醫師（美國說法。不是實習醫生 intern。台灣說內科醫師；中國大陸較常說內科醫生）