The medical specialty dealing with the diagnosis and non-surgical treatment of internal diseases. Often contrasted with 外科学 (surgery).
He majored in internal medicine and became an internist.
Textbooks on internal medicine are very thick.
内科 is the clinical department or field of internal medicine in a hospital setting, while 内科学 is the academic discipline or science of internal medicine.
Compound of 内 (internal) + 科学 (science), a straightforward modern coinage for the medical specialty.