Have a look at the video below to get a good idea of what data management is, or should be.
As you can see, RDM refers to any action that takes care of data before, during and/or after research.
Research Data Management is the compilation of many small practices that make your data easier to understand, less likely to be lost, and more likely to be usable during a project or ten years later.(Briney. 2015. Data Management for Researchers. Pelagic Publishing Ltd.)
These many small practices include everything you see on the picture below: