A Data Management Plan (or DMP) is a formal document required by many federal and private funding agencies that provides information on the data you will be collecting through the course of your project. Typical elements include a description (provides subject scope and scale), probable formats, metadata, how the data will be stored, secured and backed-up, who will be primarily responsible for the care of the data, and how the data will be preserved and shared with a broader audience.
Keep in mind that Duke does have its own policy relating to data sharing, retention and ownership. You will want to ensure that what you put in your DMP aligns with this policy. Note that Appendix P (PDF document) of the Duke Faculty Handbook contains the full text of this policy as well as many others that impact research.