Definition - What does Fatal Error mean?
A fatal error is an error that causes a program to terminate without any warning or saving its state. A fatal error, upon occurring, aborts the application currently running, and may cause the user to lose any unsaved changes made in the program. Exact reasons for fatal errors are very difficult to determine.
A fatal error is also known as a fatal exception error.
Techopedia explains Fatal Error
A fatal error occurs when an application tries to access invalid data or code, an illegal action is attempted or an infinity condition is met. The program shuts down and returns the user to the operating system. An operating system keeps a log of the information related to the error for the user to view the details and determine possible causes of the fatal error. Similarly, in some cases the image of a process (core dump) is also sometimes maintained by the OS in the event of a fatal error.