Please explain fellowships internships

Dear friends,

I need help with understanding the nature of fellowships and internships.
Why is the first year of residency called an internship? Do you work for free that year? Is it an additional year added to your residency?

Fellowships: What are they? Does everyone have to do one after they finish their residency?
Thank you!

Calling the first year of residency 'internship' is in some respects just a tradition. Different specialties require different things for the first year…sometimes they are rotating in which you spend a couple of months in several different areas. Sometimes you spend the first year with the general surgery residents and then move on to your particular specialty in the latter years. As far as I know, all internships are paid.
A fellowship is not required. Fellowships are for people looking to further specialize. For example, to be a board-certified cardiac surgeon you would need to first complete a residency in general surgery and then complete a fellowship is cardiac (or cardiothoracic) surgery. You could just stop after your residency in general surgery and be a general surgeon without doing any fellowship.
For a list of the different residencys and fellowships available, check

Once again you have rescued me from ignorance. For that I am ever so grateful.