You need to turn in a thesis prospectus for obtaining a MS or PhD degree. The department has official guidelines as of what to turn in and such.
In terms of content, both MS and PhD prospectus need to discuss the research to be conducted (literature review, proposed methods, etc). In addition, the PhD prospectus also requires you to propose the courses you are going to take (refer to Course & Degree Requirements for info on the major and minor courses).
MS Thesis Prospectus Requirement
"The prospectus should be a clear and well-organized preliminary report. It should contain (1) an introduction to the subject, giving a brief general statement of the field of interest and a concrete statement of the limited area of work which it is intended to undertake; (2) a review of relevant background information; (3) the proposed method of solution; (4) a tentative time schedule for completion of the work; (5) the name of the faculty member who will act as thesis advisor, and reader to be selected by the student with the concurrence of the advisor; (6) signatures of thesis advisor and reader to indicate approval of the proposed research project. Either the thesis advisor or the reader must be a member of the faculty of the Nuclear Science and Engineering Department."
Reference: http://web.mit.edu/nse/education/grad/ms.html#thesis
PhD Thesis Prospectus Requirement