Hids and Xenon lights are the same. Or more accuratly, Xenon lights fall under the range of High Intensity Discharge lights. Instead of a filiment, like used in normal halogens, Xenon lights produce an Arc of electricity. This arc passes through a tube that is filled with Xenon gas and metallic salts. Think of it as a constant camera flash.
"Fake hids", which I believe would encompass PIAA and Sylvania bulbs, still use Xenon gasses to produce the bighter lights, but (and I think..) still use a filimant and normal housing unit. This way you can have the appearance of HIDs without the same projection setup.