Parchment paper, also known as baking parchment or silicon paper, is a relatively new addition to the North American kitchen utensil scene, but it is extremely handy. Once you've used it, you'll wonder how it is you've lived without it for so long.
Parchment paper is a heavy brown paper which has been treated with supfuric acid to make it grease, moisture, and heat resistant, and then coated with silicone to make it non-stick. I'm sure you're already imagining the multitude of uses you could put such a product to.
Some suggestions: Line cookie sheets and cake pans with parchment paper before baking: the cookies will slide off, the cake will fall out, without sticking to the pan. Easy to clean up, too; just toss out the parchment. (You can re-use it several times first.) Experience will help you decide whether you need to oil the parchment paper first. For cookies, it's often not necessary, and in fact those which are prone to spreading - Toll House cookies, for example - will benefit from ungreased parchment, and will form a nice ridge along the edge when baked instead of a thin, burnt flat bit. For cakes, I often cut out a piece of parchment to fit in the bottom of the pan and then grease and flour it, if that's what the recipe calls for with the cake pan. Parchment paper is also used to wrap foods, primarily meat, to be baked en papillote, that is, baked inside a wrapping.
You can - and probably should - use parchment paper instead of plastic wrap to wrap foods that will be microwaved. You can also use it to keep your counters clean when rolling out pastry; just put a big sheet on the surface, plop the dough down, cover with a second sheet, and roll. You don't need to put flour on it; the dough won't stick. I've even heard that you can line a frying pan with parchment and make scrambled eggs with no butter, but haven't verified this, and anyway, I like the taste of butter in my scrambled eggs.
You can substitute waxed paper or greaseproof paper for parchment paper on the bottom of cake pans or on your counters for rolling, but not when baking cookies, microwaving, or preparing something en papillote. In these circumstances waxed paper, unlike parchment, will burn.
You can buy parchment paper fairly easily these days in gourmet shops and often in supermarkets, where tin foil and waxed paper are sold. It's sold in sheets and rolls; if buying the latter, be sure it's wide enough to be truly useful. A narrow piece just has to be overlapped with another to cover a cookie sheet or roll out a pie crust. | 
