noun
A5 paper size (148mm x 210mm)
Standard paper size used for notebooks, booklets, and documents. The dimensions are 148mm by 210mm.
このノートはＡ５判で、持ち運びに便利です。
This notebook is A5 size, convenient for carrying around.
Ａ５判の用紙に印刷してください。
Please print on A5 paper.
A4 is larger (210mm x 297mm), commonly used for office documents and letters.
B5 is slightly larger than A5 (176mm x 250mm), often used for textbooks and magazines.
From the ISO 216 A-series paper size standard, where 'A5' indicates the size, and 判 (はん) meaning 'size' or 'format'.