Paperback
A paperback (softcover, softback) book is one with a thick paper or paperboard cover, and often held together with glue rather than stitches or staples. In contrast, hardback (hardcover) books are bound with cardboard covered with cloth, leather, paper, or plastic.
Inexpensive books bound in paper have existed since at least the 19th century in such forms as pamphlets, yellowbacks, dime novels, and airport novels. Modern paperbacks can be differentiated from one another by size. In the United States, there are "mass-market paperbacks" and larger, more durable "trade paperbacks".