You need to turn in a thesis prospectus for obtaining a MS or PhD degree.
Overview
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, last accessed August 2014
PhD Thesis Prospectus Requirement
"This prospectus should be a few typewritten pages long and should contain a descriptive title of thesis; the date of general exam; signatures of doctoral supervision committee members, including supervisor(s) and faculty reader; general description of the problem; its significance; and background information relating to the problem. Thesis registration is permitted in the term the General Examination is successfully completed, and the prospectus is to be submitted no later than the end of the first term of thesis registration; failure to comply will result in refusal of thesis registration in further terms until an approved prospectus is submitted. An approved copy of the form listing the subjects to be taken to satisfy the advanced subject and minor requirements (48 units) must be attached to the thesis prospectus for review by the thesis supervisor. One copy of the approved prospectus must be submitted to the NSE academic office.
After submittal to the NSE academic office, the prospectus should be sent electronically to NSE faculty members for their review. Unless informed to the contrary within one month after submittal, the candidate may assume the prospectus has been accepted. If the prospectus is considered unacceptable, the candidate will receive, within one month of submittal, a written statement to the effect from the supervisor acting for the department. If this occurs, another prospectus must be submitted for approval."
Reference: http://web.mit.edu/nse/education/grad/phd.html, last accessed August 2014