Thanks! This looks really useful.
Anyway, the 'hide' is part of a creature (NPC or PC) that stores characteristics (such as undead properties, construct properties, etc) by default (it's visible in the toolset if you open up a creature's inventory, it's in the secondary equipment tab thing). The PRC and some modules use the hide for more advanced purposes (the PRC might use it for psionics related things, for instance, or extra properties from a prestige class, etc) and a module might use it for, well, like the stuff I mentioned (faction reputation, other things that the game can't track via normal methods).
(Off topic, but this was part of the issue that the spell Anti-Magic Zone had before it was fixed. It was nuking the hides of some classes, like liches, and basically breaking them. xD)
