The blue screen of death (BSoD) – or blue screen error, blue screen, fatal error, bugcheck, and officially known as a stop error – is a critical error screen displayed in many iterations of Windows, a series of operating systems by Microsoft. It is used to indicate a system crash, in which the operating system reaches a critical condition where it can no longer operate safely. Its name comes from the blue-colored background used predominantly on the error screens found in the majority of Windows releases, which was changed to black starting with Windows 11 version 24H2.