Answer: endpapers

AnswerCrossword Clue
ENDPAPERSThey're inside the covers
ENDPAPERSInside covers
ENDPAPERSParts of a book.
endpapersENDPAPER, a sheet of paper used in bookbinding
endpapersA blank or decorated leaf of paper at the beginning or end of a book, esp. one fixed to the inside of the cover