Paperback books are a type of book that have a flexible cover made of paper or cardstock. They are typically lighter and more affordable than hardcover books, making them a popular choice for readers. The pages are usually glued together at the spine, which allows the book to be easily opened and read. These books come in various sizes and formats, including mass market paperbacks and trade paperbacks. Mass market paperbacks are smaller and often sold in supermarkets and convenience stores, while trade paperbacks are larger and usually found in bookstores. Both types are widely used for fiction and non-fiction titles.