noun
small-format paperback; pocket paperback
Refers to the compact, affordable paperback format common in Japan, typically A6 size, often used for reprints of novels and light novels.
通勤中に文庫本を読むのが好きです。
I like reading pocket paperbacks during my commute.
Compound of 文庫 (bunko, 'library' or 'book collection') and 本 (hon, 'book'), referring to a book format originally designed to be compact and collectible.