Softback is a term often used to describe a book with a flexible cover. However, there are various synonyms, which you can use for a softback. A popular synonym for softback is paperback, which is also used to describe a book with a flexible cover. Another synonym is trade paperback, which is often used to describe books with a larger format or higher quality cover than typical paperbacks. Mass-market paperback is another term for softback, which implies that it has been printed in large quantities for the general public. Other synonyms to consider include flexible binding, pocket book, and sewn binding. Ultimately, the best term to use depends on the book's size, aesthetics, and purpose.