Stands for Halo 3 Disc Read Error. When you boot up your Halo 3 and all you get is a "Disc Read Error" message causing you to slam your head into a wall. After waiting for such a hyped up game you should be able to play with no problems.
I just bought a new 360 and Halo 3 but sadly upon starting up a matchmaking game on snowbound, i am a victim of H3 DRE. Thanks Bungie for this awesome game! Now im going to throw my 360 out the window and hang myself.