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.

Fair : is a worn book that has complete text pages (including those with maps or plates) but may lack endpapers, half-title, etc. (which must be noted). Binding, jacket (if any), etc., may also be worn. All defects must be noted. (defined by AB Bookman's Weekly)