paper cover; paperback
Refers to a book bound with a paper cover, as opposed to a hardcover. Can mean the paper cover itself or a paperback book.
この小説は紙表紙で出版された。
This novel was published in paperback.
紙表紙の本は軽くて持ち運びやすい。
Paperback books are light and easy to carry.
Compound of 紙 (kami, 'paper') and 表紙 (hyōshi, 'cover'), literally 'paper cover'.