There are many ways to define service-learning.  The Maryland State Department of Education (MSDE) defines it as follows:

Service-Learning is a teaching method that combines meaningful service to the community with curriculum-based learning. Students improve their academic skills by applying what they learn in school to the real world; they then reflect on their experience to reinforce the link between their service and their learning. -- Learning in Deed

Service-learning different than:

 Volunteerism:  Volunteers engage in service for a variety of personal reasons.  They do not necessarily link their service to academic studies nor do they receive academic credit for their efforts.

Community Service:  People engaging in community service do so for a variety of reasons.  This is a broad term that can encompass court ordered, stipended, or volunteer service.  It also does not necessarily link to academic studies.

Work Study Internship:  Student interns frequently work at for-profit businesses to benefit the financial standing of that business.  They are not necessarily working to improve their communities through these internship experiences.  There can be overlap between work study internships and service-learning.  Students are engaging in service-learning, if, through their internship experiences, they work to improve the health or welfare of their community while making the link to their academic studies.