It's perfectly reasonable what you're asking, I made that vague to discourage people from even trying anything they might be worried crosses the line but I am not surprised someone wants clarification.
Obscene content is basically something like gore, obviously pornographic images (this isn't a porn sharing site), anything depraved like shit and whatnot, you know, that sort of stuff.
As for porn dump threads, it's just to make it clearer we ain't a porn site. By definition you shouldn't be posting blatantly pornographic images (I'll leave what is pornographic up to the user, I think people should be able to have some judgement on that). But as for the cutoff limit, the short answer is 1 basically.
I try to be relatively lenient with this stuff, I just don't want this to be fapchan/gurochan anything of that sort.