noun
octavo; 8vo
A book format where each sheet is folded into eight leaves (16 pages). Used in publishing and bibliography.
この本は八つ折り判で、手に持ちやすいサイズです。
This book is in octavo format, a size that's easy to hold.
古い聖書は八つ折り判で印刷されることが多かった。
Old Bibles were often printed in octavo.
From 八つ折り (yatsuori, 'folding into eight') + 判 (ban, 'format/size').