1. [techspeak] An error in which a running program attempts to access
memory not allocated to it and core dumps with a segmentation violation
error. This is often caused by improper usage of pointers in the source
code, dereferencing a null pointer, or (in C) inadvertently using a
non-pointer variable as a pointer. The classic example is:
scanf ("%d", i); /* should have used &i */
2. To lose a train of thought or a line of reasoning. Also uttered as an
exclamation at the point of befuddlement.
The Free On-line Dictionary of Computing (30 December 2018):
An error in which a running Unix program attempts to access
memory not allocated to it and terminates with a segmentation
violation error and usually a core dump.