slip sheet

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   A strong, thin pallet-sized sheet of plastic or fiberboard used to transport heavy items.
3. 3
   A sheet inserted between freshly printed pages to prevent them from sticking together.