noun
pocketbook; small paperback
A small, portable book, often a paperback, that fits in a pocket. Used similarly to English 'pocketbook'.
旅行中はポケットブックを一冊持っていく。
I take one pocketbook with me when traveling.
文庫本 is a standard Japanese small-format paperback, while ポケットブック is a loanword often used for Western-style pocket-sized books.
Borrowed from English 'pocketbook'.