Internships are more closely supervised at the work site and a faculty member may supervise, as well. You may also receive academic credit for internships, since there is a learning component. The only real similarity between unpaid internships and community service is that they are both unpaid experiences. Internships are more closely related to your career goals rather than giving something back to the community. In community service, the person being served has the most to gain from the experience.
Internship also has a learning component and is closely monitored.
It maybe monitored by a direct supervisor at the site and a faculty member. These are also closely supervised, learning experiences. These experiences are usually always unpaid. Also, the fields that are associate with fieldwork and student teaching are quite different from those that internships are abundant. Fieldwork and student teaching are usually associated with the social service, nonprofit, or government fields.