Mass market paperback : Also known as the pocket paperback. A small format paperback usually measuring about 4" by 6".

spine : The outer portion of a book which covers the actual binding. The spine usually faces outward when a book is placed on a shelf. Also known as the back.

acceptable : A non-traditional book condition description that generally refers to a book in Good or Very Good condition, although no standard exists for this term, and the word can be used to describe a wide variety of actual book conditions.