Bunkobon

In Japan, bunkobon (文庫本) are small-format paperback books, designed to be affordable and space-saving.

Modern bunkobon can include bestsellers and works of scholarship alike and their pocketbook size make them useful while commuting.

[2] They are used for similar purposes as Western mass market paperbacks: generally for cheaper editions of books which have already been published as hardbacks.

The original Iwanami Bunko series is credited for transforming books in Japan into affordable, mass-market commodities.

[1] The bunkobon format began to flourish during the late 1920s, following the development of printing technology able to mass-produce cheap books and magazines.