A book bound in heavy paper or light card covers trimmed to the size of the pages. Originally used for novels in the late nineteenth century. Paperbacks now form the bulk of the personal book buying market, both for fiction and non-fiction.
A binding with a soft cover, usually a light cardboard. A trade paperback is usually the same size as a hardcover book, and printed to the same standards. A mass-market paperback is usually smaller, designed to fit in a rack, and printed on cheaper paper.
Paperback (sometimes softback, or softcover) may refer to a kind of book binding by which papers are simply folded without cloth or leather and bound - usually with glue rather than stitches or staples - into a thick paper cover; or to a book with this type of binding. (Contrast cloth, hardback, hardbound or hardcover.)