Digital Rights Management - also known popularly as DRM is a technology which can be used to restrict or control how and by what medium a content can be viewed by a user. And it forms the basis by which media industry hope to implement and safeguard their hold on the copyright of the content they generate - be it music, video or any piece of software. Not surprisingly, RMS and his ilk consider DRM a threat to the very ideology and freedom for which GNU stands for. So you have the GPL v3 draft which comes down heavily on anything even remotely related to DRM and hopes to incorporate safeguards against DRM in the new version of the licence itself.
DRM also known as trusted computing can be used to create a way for companies to trust your computer with their copyrighted material. fsfe.org has an enlightening article which throws light on DRM, Trusted computing and how it could adversely affect out lives. The author pursues the pros and cons of allowing DRM technologies in ones computer.