[quote user="KiiLLER ViRUS"]but what is it?[/quote]DRM stands for Digital Rights Management. It allows publishers control over the content license you purchase. DRM is the thing that ties movies you buy from iTunes to your account or games you buy on the
Live Marketplace to your gamertag.
For PC games, DRM's been around for ten years in the form of Valve's Steam platform. Games bought on Steam are typically tied to the account they're purchased from and protected with DRM so that they cannot be freely copied to another PC and played.
The downside to DRM is that there is no secondary market. Game licenses cannot be resold from person to person. They can't even be given away. MS was attempting to bridge physical copes with DRM, though the downside was that games would only be playable
for up to 24hrs when not connected to Live. This bothered many people, people who seem to forget that Steam had no easy to use offline mode when it first launched, either.