As defined by Answers.com, Digital Rights Management is ..
A system for authorizing the viewing or playback of copyrighted material on a user's computer or digital music player. DRM has centered around copyrighted music, with Apple's FairPlay and Microsoft's Windows Digital Rights Manager being the two predominant DRM systems. Video DRM is on the horizon as broadband Internet and more highly compressed video formats take hold. See FairPlay, Windows Digital Rights Manager and copy protection.
Wikipedia goes into greater detail concerning the general controversy.
Digital Rights Management is a controversial topic. Advocates argue DRM is necessary for copyright holders to prevent unauthorized duplication of their work to ensure continued revenue streams. Some critics of the technology, including the Free Software Foundation, suggest that the use of the word "Rights" is misleading and suggest that people instead use the term Digital Restrictions Management. The position put forth is that copyright holders are attempting to restrict use of copyrighted material in ways not granted by statutory or common law applying to copyright. Others, such as the Electronic Frontier Foundation consider some DRM schemes to be anti-competitive, citing the iTunes Store as an example.
Obviously, anyone who creates their own content, either music or video or even software should have the rights to control and profit from it's distribution. But where will the control be placed, in the hands of the consumer or the corporation?
Update: More About Digital Rights Management
2007/01/28 - Here are a few more resources concerning DRM that will help. Pay particular attention to the first link from Slashdot.org concerning a call-to-action for everyone.