If you're asking what the meaning of the acronym
rc is, according to the jargon file, it derives from runcom:
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).
In version 7 Unix the
/etc/rc's were replaced with runlevels. So on a modern day Linux box you'll see this type of directory structure.
The runlevel system replaced the traditional /etc/rc script used in Version 7 Unix.
$ ls -l
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 init.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc0.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc1.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc2.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc3.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc4.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc5.d
drwxr-xr-x. 2 root root 4096 Jan 3 12:21 rc6.d
Each of these directories represents a runlevel. Different distros use these in slightly different ways. For example, on Red Hat based distros run level 3 is meant for running a system without a desktop, while 5 is meant for when running a desktop.
To designate that you wanted a particular service to start in one level vs. not in another you'd initially have to create links to the actual
rc scripts for a particular service, naming the link in a special way. The links would look like this:
$ ls -l rc3.d/
lrwxrwxrwx. 1 root root 20 Dec 7 20:56 K50netconsole -> ../init.d/netconsole
lrwxrwxrwx. 1 root root 18 Dec 7 20:56 K85ebtables -> ../init.d/ebtables
lrwxrwxrwx. 1 root root 17 Dec 7 20:56 K90network -> ../init.d/network
lrwxrwxrwx. 1 root root 28 Jan 3 12:21 S04dkms_autoinstaller -> ../init.d/dkms_autoinstaller
lrwxrwxrwx. 1 root root 15 Dec 14 22:57 S95jexec -> ../init.d/jexec
Names starting with a
K meant that this service should be killed for this runlevel, while
S meant that it should be started. The numbers after the
S denoted what order the services should be killed and started.
In recent years this approach has started to wain in favor of 2 new technologies,