This page collects some useful tips.
A core file or core dump is a file that records the memory image of a running process and its process status (register values etc.). Its primary use is post-mortem debugging of a program that crashed while it ran outside a debugger. A program that crashes automatically produces a core file, unless this feature is disabled by the user.
This topic is too large to be discussed here (see the gdb and Wikipedia links).
If you just want to find out what caused the crash, here is how with
$ file core.111506 core.111506: ELF 64-bit LSB core file x86-64, version 1 (SYSV), SVR4-style, from '/fast/users/szyskam_c/work/miniconda/envs/fastq_search-env/bin/python3.7 -m sna'