RROD is the instance when your console overheats and the GPU is warped away from the motherboard. In human-speak that means total system failure. I've lost 8 360s to this problem.
The problem with the Launch 360s, called "Xenons", was that the GPU was placed directly underneath the DVD drive. As games and movies sped up and got hot the console couldn't control the heat and the metal clamps holding the GPU down into the motherboard would warp and cause the GPU to disconnnect from the system. The only way you could fix was to either send it to Microsoft Offices in PA, AZ, or TX and in 3-7 weeks you could get a new or fixed console (for $99.99 or free with warranty), OR you could open up the casing and sauder yourself some new brackets for your GPU if you had the know-how.
After Millions of dollars were spent in repairing and replacing 360s Microsoft re-arranged the motherboard for the 360 and released NEW consoles called "Jaspers." These NEW consoles had smaller power-bricks that used less wattage and had the GPU placed far away from the DVD drive. RRODs still popped up but not as bad as the Launch consoles.
With the release of the Kinect (Project Natal) the power wattage increased within the console. I knew that RRODs would pop up again, but I kept my mouth shut in hopes it wouldn't. Using USB connection and powering itself from the 360 it was inevitable that RRODs would happen. Not to mention the massive number of people who DO NOT know how to take care of their consoles.
Watch THIS video on how to take care of your 360.
Now I'm starting the rumour that Microsoft will unveil the "Valhalla" motherboard. A Stream-lined motherboard, a smaller more effective power-brick, and maybe another fan. I wouldnt be surprised if Microsoft talks about it or even shelves it.