Afaik, this is some sort of debug output. Either one of your compiles had failed at some point, or when you rebooted something didn't close properly (can happen), or something similar occurred with some open file(s) at some point (like closing a terminal during a compile, etc).
The core files are similar to FILECHK.00x files in Windows. Unless you're a programmer, I don't think this file is of any use to you. When I get them, I just delete them (the same way I do with FILECHK files). Most likely nothing is broken, but if it is, you'll find out soon enough anyway, and can then take appropriate steps. Even if something was broken, it would most likely be an individual program, rather than the OS as a whole.
I wouldn't worry, if I was you, but anyone who knows better can certainly correct me