Overview
The bomb icon (💣) has several different applications in computing, and typically indicates a fatal system error.
In computing
Mac OS
The bomb icon in Mac OS is a symbol designed by Susan Kare that was displayed inside the System Error alert box when the "classic" Macintosh operating system had a crash which the system decided was unrecoverable. Since the classic Mac OS offered little memory protection, an application crash would often take down the entire system.
The bomb symbol first appeared on the original Macintosh in 1984. Often, a reason for the crash, including the error code, was displayed in the dialog. In some cases, a "Resume" button would be available, allowing the user to dismiss the dialog and force the offending program to quit, but most often the resume button would be disabled and the computer would have to be restarted. Originally, the resume button was unavailable unless the running program had provided the OS with code to allow recovery. With the advent of System 7, if the OS thought it could handle recovery, a normal error dialog box was displayed, and the application was forced to quit. This was helped by the classic Mac OS providing a little bit of protection against heap corruption using guard pages; if the application was to crash and the application's heap was corrupt, it could be thrown away.
From Wikipedia (CC BY-SA 4.0).