<p>It is not uncommon in some fields for an internship to be unpaid. If it’s called an internship, then it is an internship, not “volunteering.” The distinction, I believe, is that an internship is supposed to help you develop professionally, while volunteering could mean any number of things. Which is not to say that interns are always doing relevant, educational work, but that is the point. </p>
<p>It is possible to have a paid volunteer position, although you are given a “stipend” instead of wages/salary usually well below minimum wage. Gets a bit fuzzy, I guess.</p>
<p>I considered research opportunities - paid or not - as internships, not volunteering activities, since technically you’re learning skills, opportunities to use your research in competitions, working on a project that’s more or less your own, etc.</p>