You’ve got me thinking about this now because I’ve been drinking
I think you’ve got 3 main sub-genres of horror: slasher, monster, and supernatural.
Things get murky (but fun!) when movies combine genres.
Examples IMO:
- Aliens = Sci-fi (main genre) + Monster horror (sub)
- Jaws = Thriller (main genre) + Monster horror (sub)
- Scream = Mystery (main genre) + Slasher horror (sub)
- Sixth Sense = Thriller (main genre) + Supernatural horror (sub)
- Silence of the Lambs = Thriller (main genre) + Slasher horror (sub)
- Cabin in the Woods = All Horror genres (main) + comedy (sub)
- Event Horizon = Supernatural horror (main genre) + SciFi (sub)
Etc. You get the point.