I suppose it could be all the examples you listed pretty much.BTW, what is "monster" in context of this thread? Is it everything non-human? Is it anthropomorphed animals? Is it animals with some human-like bodyparts? Is it sentient animals?
What about elves/dwarves/gnomes/...? In some sources these DO counts as (at least) demihumans.
Edit: does Nyaruko counts as monster-girl? Yes, she is monster in her monster form, but in her human form there's nothing "monster"... 😕
I suppose it could be all the examples you listed pretty much.