An extern is usually a med student assigned to a medical or surgical service to substitute for an intern on vacation or to supplement the number of interns when there are lots of patients on that service. Externs don't live in the hospital, but stay there the nights they're on duty. Internship is the first year after medical school and is required for licensure by most states. The word was assigned to this job because in the good old days, interns stayed in the hospital every day and every night for the whole year and couldn't be married. Those days are gone, thank goodness.
