ejiki: Well, wikipedia says
Digital Rights Management (DRM) is a class of technologies that are used by hardware manufacturers, publishers, copyright holders, and individuals with the intent to control the use of digital content and devices after sale;] there are, however, many competing definitions. With first-generation DRM software, the intent is to control copying; With second-generation DRM, the intent is to control executing, viewing, copying, printing and altering of works or devices. The term is also sometimes referred to as copy protection, copy prevention, and copy control, although the correctness of doing so is disputed.
ejiki: So, In case of a game, I think that everything that does not allow you freely copy or play game - is DRM.
^this. In the US, I think you'd be in legal deep water if you tried to circumvent anything that allows you to freely copy or play a game without the express permission of the copyright holder due to the Millennium Digital Rights Act.