bashrc... vimrc.... nanorc... What does RC stand for?
If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but have not love, I am nothing. 1 Corinthians 13:2
They are runtime configuration (hence the rc) files. When you launch the associated program, it looks at the rc file for non-default user settings. Most programs work w/o such a file, either using default settings or creating the file on first use.