The Jargon File (version 4.4.7, 29 Dec 2003):

segmentation fault
 n.

    [Unix]

    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:


       int i;
       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):

segmentation fault
segfault

   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.

   [Jargon File]

   (1994-12-15)