slip sheet

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A blank sheet of paper slipped between newly printed sheets to prevent offsetting.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun roofing Sheet material, such as reinforced kraft paper, rosin-sized paper, polyester scrim or polyethylene sheeting, placed between two components of a roof assembly to ensure that no adhesion occurs between them and to prevent possible damage from chemical incompatibility, wearing or abrasion of the membrane.
• noun shipping A strong, thin pallet-sized sheet of plastic or fiberboard used to transport heavy items.