noun
octavo format; cutting into 8 parts
Refers both to a specific paper size (about 21.5 × 16.5 cm) and to the act of dividing something into eight equal pieces. The paper size is the most common modern usage.
この本は八つ切りサイズで印刷されている。
This book is printed in octavo format.
ケーキを八つ切りにして皆で分けた。
We cut the cake into eight pieces and shared it.
Refers to quarto format or cutting into four parts, whereas 八つ切り is octavo or cutting into eight.
Compound of 八つ (yatsu, 'eight') + 切り (kiri, 'cutting'), literally 'cutting into eight'.