Cellulose powder - says so right in the ingredients, alongside lipase, calcium chloride, and potassium sorbate: http://www.garycameron.org/files/2012/04/Kraft-100-Parm-q50....

Even better, it says "The label doesn't just say parmesan, it says 100% parmesan. That's because we only use the finest ingredients, carefully crafted and aged for a sharp, distinctive taste that enhances your favourite dishes - a taste that's 100% real, 100% parmesan."

They can get away with it because "parmesan" doesn't actually mean anything outside of the EU.

Edit: As that other poster just pointed out, maybe it does mean something in the US (that label was from Canada), since someone's actually facing criminal charges for it.