A Data Management Plan (DMP) is a 1-2 page summary explaining how you plan to manage the data gathered in the course of your research project.
Most funding agencies require researchers to submit a data management plan as part of their grant application; Detailed procedures for data collection, plans for dissemination, etc.
This guide serves as a resource to completing your DMP.
If you're not already a pro, check out MANTRA's free online course for Research Data Management Training.
The following is based on NSF general plan guidelines: