A cookie sheet is usually metal, rectangular in shape, shallow depth or completely flat--kinda like a pizza pan, only rectangular.
By oven paper, are you referring to parchment paper? I went to my cabinet & pulled my box. The first thing I find wrong with this product is that mine is made by Reynolds (just kidding--sorta). Mine is made by Reynolds in France and cannot find anywhere what it is actually made out of. My box does say that it withstands temps up to 420 F, not to use under broiler, in toaster oven, or in halogen light ovens--and an obvious one--do not touch parchment paper to open flame. I suppose we could go to the website (reynoldskitchens.com) or call 1-800-433-2244 to inquire how the paper is made etc.
I would guess it's much safer than aluminum. I would even feel better about laying it on top of the aluminum baking surface.