Answer:
Parchment paper -- which is available bleached and unbleached -- is coated with silicone, while wax paper is coated in, you guessed it, wax. Soybean or paraffin wax, to be precise.
Their coatings give them different uses. Parchment paper's silicone coating makes it heat-resistant and nonstick. Line baking pans with this paper wonder and food won't stick to the pan. This trick can't be duplicated with wax paper because the wax will melt, which makes it useless as a nonstick barrier and ruins whatever you're cooking.
