The Free On-line Dictionary of Computing (30 December 2018):

run commands

    The expansion of the file name suffix, "rc",
   common to many Unix configuration files, e.g. .newsrc,
   .cshrc, .twmrc, elmrc, etc.  Always abbreviated to /R C/ when
   spoken.  Note, "rc" is not a typical filename extension as it
   doesn't start with a dot.

   The suffix "rc" derives from a script-creation utility in CTSS
   called "runcom".

   Unix FAQ

(http://cis.ohio-state.edu/hypertext/faq/usenet/unix-faq/faq/top.html).

   (2014-11-19)