What is the Difference Between Paperback and Pocket Book?

What is the difference between paperback and pocket book? The main difference is size and portability: pocket books (also called mass-market paperbacks) are smaller books measuring around 4.25″ x 6.87″ designed to fit in pockets, while standard paperbacks are larger at 5.5″ x 8.5″ or 6″ x 9″ with better print quality and durability.