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.

remainder mark : Usually an ink marking of some sort which indicates that the book was designated a remainder. In most cases, it can be found on the edges of the text block in the form of a marker stripe or a stamp of some sort.

Remainder marks considerably lower the overall collectibility of a title, although, in some cases, they are acceptable to a collector.