Rc

rc stands for runcommand. Historically UNIX boots from a file called /etc/rc which gets run from the process init, here it mounts filesystems, and starts services.

In Linux RHEL there is a /etc/rc.d/rcX.d directory which allows one to start and kill services at whatever runlevel the system runs at. If you boot into runlevel 3 then this would be /etc/rc.d/rc3.d, the file is linked from /etc/rc.d/init.d where the rc script resides.