A screen that appears on all versions of Windows when the system has an error so bad it has to shut down. The error text is displayed as DOS text on a blue background, hence the name. Versions before XP were notorious for giving this screen VERY frequently, though later versions were progressively more stable. XP and Vista users generally don't get this unless:
1. They fuck with software in ways they're really not supposed to.
2.They build their computer themselves and install vital parts wrong.
3. They use bad drivers, especially with their video cards or motherboards.
I started up Windows 95 and got the Blue Screen of Death before I even logged in!