segmentation fault

A segmentation fault (aka segfault) is a common condition that causes programs
to crash; they are often associated with a file named core.

Segfaults are caused by a program trying to read or write an illegal memory
location

In computing, a segmentation fault or access violation is a fault, or failure
condition, raised by hardware with memory protection, notifying an operating
system the software has attempted to access a restricted area of memory.

On standard x86 computers, this is a form of general protection fault. 

Segfaults are caused by a program trying to read or write an illegal memory location