Internship report contains the details of all the work that you did during your internship. The internship is a learning experience for all the people who undergo it. The purpose of any internship is to help you get acclimatized to the style of functioning of any industry. The internship helps you understand the various aspects of any job. There are times when the bookish knowledge about a certain career might not come to rescue in actual on-the-job scenarios. Internships give you that experience.
Internship report tells about all that you did during the course of the internship. Sometimes, during an internship you are given some specific assignment. The internship report, then, is supposed to include a description of the assignment that you completed during the course of the internship. The details should include a clear aim that you were working with. You could also include how you proceeded with the assignment, what kind of research went into it, and what were your observations. If you feel that you have a new idea that you thought about during the course of the internship you should definitely pitch it to your seniors at work.
Having a good internship report is important because it explains what all you have gathered from any internship. Many organizations demand their interns to present the internship report before the official completion of the internship. The purpose that this serves is also to let the employers know what the intern has gathered from the internship. If the intern comes across as someone with intelligent inputs the company might be interested in hiring him/her.