Like in OpenRC.
I believe it's "Run Commands".
But I could well be wrong as I have no idea from whence that entered by brain ?
That's right :
https://wiki.gentoo.org/wiki/Rc
the /etc/rc.d and similar usage predates plan 9 by many years see eg
https://unix.stackexchange.com/questions/111611/what-does-the-rc-stand-for-in-etc-rc-d (https://unix.stackexchange.com/questions/111611/what-does-the-rc-stand-for-in-etc-rc-d)
Typically refers to the initialization process of an RC (Resistor-Capacitor) circuit in electronics.