also: あいし
noun
interleaf; slip sheet; paper between prints
A sheet of paper placed between freshly printed pages to prevent ink transfer or smudging. Used in printing and publishing contexts.
印刷所では、刷り上がったばかりのページの間に間紙を挟む。
At the printing shop, they insert interleaves between freshly printed pages.
この本には、図版の保護のために間紙が使われている。
This book uses slip sheets to protect the illustrations.
Compound of 間 (あい, 'between') and 紙 (がみ, 'paper'), literally 'between-paper'. The reading あいし uses the on'yomi of 紙.