means A trainee who works at a company or organization, often for low pay or no pay, to gain practical experience in a field.

from From the Latin internus, 'inward, internal,' the same root behind 'internal' and 'interior.' The word first meant 'confined within' — and indeed 'intern' as a verb still means to confine someone (as in wartime internment camps). The medical 'intern,' a resident doctor living and working inside the hospital, emerged in the late 19th century, the idea being someone kept within the institution to learn its workings. From medicine the sense spread to any apprentice taken inside an organization to be trained — and, eventually, to fetch coffee.