What medical term means "within the body"?

The medical term meaning “within the body” is internal.

Internal comes from the Latin internus, meaning “inside” or “inward.” In medicine and anatomy, it describes something located inside the body, occurring within an organ, or arising within an organism. Internal organs include the heart, lungs, liver, and kidneys.

The word is often contrasted with external, which refers to the outside of the body. It can also describe medical treatment: an internal medicine is taken into the body, usually by swallowing, rather than applied to the skin. In anatomical language, “internal” may also mean closer to the body’s center or midline, depending on context.

Internal should not be confused with visceral, which more specifically refers to organs or tissues inside body cavities. Nor is it identical to intracorporeal, a technical term meaning “within the body.” For a general medical vocabulary question, however, internal is the standard and fairest answer.