init - Wikipedia
https://en.wikipedia.org/wiki/InitResearch Unix init ran the initialization shell script located at /etc/rc, then launched getty on terminals under the control of /etc/ttys. There are no runlevels; the /etc/rc file determines what programs are run by init. The advantage of this system is that it is simple and easy to edit manually. However, new software added to the system may require changes to existing files that risk producing an unbootable system.
[OpenWrt Wiki] Init Scripts
https://openwrt.org/docs/techref/initscripts23.12.2020 · Init Scripts Init scripts configure the daemons of the Linux system. Init scripts are run to start required processes as part of the boot process. In OpenWrt init is implemented with init.d. The init process that calls the scripts at boot time is provided by Busybox. This article explains how init.d scripts work and how to create them.
Init scripts - Calculate Linux
https://old.calculate-linux.org/main/en/initscriptsThe scripts that the rc process starts are called init scripts. Each script in /etc/init.d can be executed with the arguments start, stop, restart, pause, zap, status, ineed, iuse, needsme, usesme and broken. To start, stop or restart a service (and all depending services), start, stop and restart should be used.