rc is an ancient Plan 9 abbreviation that stands for run commands. Eric Raymond's The Jargon File mentions a script of a similar name called rc file. This file contained "startup instructions for an application program (or an entire operating system)".
It would seem rc was the basis for modern init systems.
- Eric S. Raymond. http://www.catb.org/jargon/html/R/rc-file.html Retrieved on June 27th, 2015