Internship can be paid or unpaid, for credit or not credit, and can vary in many fields of job market from private to non-profit. Internship can also be locally, nationally and internationally. As a student making for an internship, you’ll sound more informed if you can describe exactly what kind of experience you want to your employer. These descriptions can also help your search and decision for an internship that is most beneficial.
Sources:
http://internships.about.com/od/internships101/f/faq5.htm
https://www.wetfeet.com/articles/defining-the-six-most-common-internship-types