Either of two folded sheets of heavy paper having one half pasted to the inside front or back cover of a book and the other half pasted to the base of the first or last page.

• 蝴蝶页，衬页两张叠起来的加厚纸的任一页，其中一页与书的封面或封底的里板粘在一起，另一页粘到首页或底页的底部