The sheet of self-adhesive decorations supplied with a set, for the builder to apply.
Many sets come with a sticker sheet in place of printed parts. Whether and how well the stickers were applied affects the value of a used set, and an unused sheet is worth having. BrickDb records it as its own line of the condition profile, from sealed and unapplied through applied in good condition to missing. Fans jokingly call it the DSS, the “dreaded sticker sheet”.