Somewhere between being a student and a professional is the life of an intern, an advanced student, especially in medicine, who gets on-the-job experience.
To intern or be an intern is to leave the classroom behind and start doing part of your profession — usually, the job of being a doctor. Sometimes an intern is paid, but not always, and the pay is never great. The experience is considered payment in itself. There have been many medical TV shows that feature interns, probably because the hours are long, the job is difficult, and there are many opportunities for drama in this boot camp for doctors. Medical interns may appreciate another meaning, which means to take away someone's freedom, as in "Why did you intern the prisoners?"