Internship is a system of on-the-job training for white-collar jobs, similar to an apprenticeship. Interns are usually college or university students, but they can also be high school students or post graduate adults seeking skills for a new career. They may also be as young as middle school or in some cases elementary students. Student internships provide opportunities for students to gain experience in their field, determine if they have an interest in a particular career, create a network of contacts, or gain school credit. Internships provide employers with cheap or free labor for (typically) low-level tasks. Some interns find permanent, paid employment with the companies in which they interned. Their value to the company may be increased by the fact that they need little to no training.
Source: Wikipedia.
Internship