I've used unix-like OS's for 28 years and I don't remember coming across it as a password.

It is a common username (see: https://en.wikipedia.org/wiki/Toor_(Unix) ), the machine I am typing this on has it.

It was the default password for the root user in Kali Linux for a while.

	▲	merpkz 32 minutes ago \| parent [-]
		Back when it was called Backtrack if my memory serves right. I remember being puzzled that it was not the case anymore one day and they even switched to regular user around when Kali became a thing