What the heck is a rc.local stop job?

[Tom Horsley]

I just rebooted my fedora 27 partition to get new kernel
running, and I had to hit the reset button because it
stuck here forever:

A stop job is running for /etc/rc.d/rc.local Compatibility

There is no bloody rc.local script that runs on shutdown,
it exists for running stuff at boot. What has systemd
done now and how do I make it stop?