I'm aware of that. I was just saying I've never heard it called a torture porn.

Torture porn includes anything that has a whit of onscreen torture, regardless of its relevance or importance to the plot.

Now someone explain the difference between a gory giallo with an obvious villain and a nearly bloodless slasher with much mystery. I would argue that many popular giallos are actually slashers, and vice versa.

We have an entire Sticky devoted to the subject:

http://horror.com/forum/showthread.php?t=33002

That is almost every single horror film then.

True, it's a meta-genre created by some old fart who hates onscreen violence (i.e. most modern horror). Although through common error, it is becoming a recognized subgenre.

Would Reservoir Dogs be considered torture porn then?

Yes, torture porn includes some crime drama, sci-fi, etc.

Every movie that has a sex scene isn't considered porn, so why would every movie that has some blood be considered torture porn?

It is by some. The old definition of porn does not reference sex specifically, which is why that same old fart used "porn" in the term "torture porn".

Giallo is a type of (Italian) who dunnit film that has certain tropes and charactertics - stylish camera work/lighting, disguised/black gloved killer, protagonist in the role of amateur detective.

Killer usually is revealed to be crazy through something that happen to them.

Obviously not all Giallo films have all of these but these are the building blocks of the genre.