The "blue screen of death" (BSOD) is an error screen displayed by the Microsoft Windows operating system when it encounters a critical system error. This screen indicates that the system has crashed and cannot continue running safely. It typically shows a blue background with white text, detailing the error and sometimes suggesting troubleshooting steps. The BSOD can be caused by various issues, including hardware failures, driver conflicts, or software bugs. When it appears, the computer usually needs to be restarted, and users may need to investigate the error code to resolve the underlying problem, ensuring the stability of their Windows system.