Survival horror seems to cover that though, with "Weak survivor character, at a disadvantage from the start", because to me that's a key element of slasher films, also, "Horror elements such as mazes, unexpected ambushes or injuries" works with that conceptually as well.

Part of the problem might be that lots of genres of horror borrow from each other or blend into each other. For instance movies like The Thing, Leviathan, and Virus, all blend elements of Body Horror (graphic dismemberment, mutations), Survival Horror (isolated or actively hostile environments, help won't be coming), and Monster Horror (inhuman antagonists, the danger of being consumed/subsumed).

This might end up being an exchange where optional details and clarifications in requests are vital. Though relying on types of horror that have TV Tropes pages is a really, really good idea. Makes it easy for people to check what each type of horror is and see examples.