The Jargon File (version 4.4.7, 29 Dec 2003):

rc file
 /R?C fi:l/, n.

    [Unix: from runcom files on the CTSS system 1962-63, via the startup
    script /etc/rc] Script file containing startup instructions for an
    application program (or an entire operating system), usually a text file
    containing commands of the sort that might have been invoked manually once
    the system was running but are to be executed automatically each time the
    system starts up. See also dot file, profile (sense 1).


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

rc file

   /R C fi:l/ [Unix: from the startup script "/etc/rc", but this
   is commonly believed to have been named after older scripts to
   "run commands"] Script file containing startup instructions
   for an application program (or an entire operating system),
   usually a text file containing commands of the sort that might
   have been invoked manually once the system was running but are
   to be executed automatically each time the system starts up.
   See also dot file, profile (sense 1).

   [Jargon File]