SIGSEGV or `kill -l 11`

SIGSEGV --- Invalid memory reference (segment fault). The possible cases of your encountering this error are:
- buffer overflow
- stack overflow
- illegal file access

man 7 signal

Standard Signals
...
Signal     Value     Action   Comment
──────────────────────────────────────────────────────────────────────
...
SIGSEGV      11       Core    Invalid memory reference