Mass-market paperback

The mass-market paperback is "a small, usually non-illustrated, inexpensive bookbinding format," around 4.25 by 7 inches in the United States and A-format, 110 by 178 mm, in the United Kingdom. The article's contrast with the trade paperback, "a higher-quality paperback book," runs on distribution as much as on quality: mass-market books are "often sold not only at bookstores, but also where books are not the main business," airports, drugstores and supermarkets, reached through magazine distributors, and their trim is sized to the spinner rack, in William Gibson's phrase "a pocket-sized slab of prose meant to fit a standard wire rack."

The pedigree is Penguin in 1935 and Pocket Books in 1939, with the wartime Armed Services Editions carrying the format worldwide. For writers it matters as an identity: Japan's equivalent is the bunkobon, close to Kanonara's A6 bunko page format, and choosing a paperback class is a trim size decision.