DJ : Short for dust jacket, a protective and often decorative wrapper, usually made of paper which wraps around the binding of a book.

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.

cocked : Refers to a state where the spine of a book is lightly "twisted" in such a way that the front and rear boards of a book do not align when the book is lying flat. Severity may differ.

cracked : In reference to a hinge or a book's binding, means that the glue which holds the opposing leaves has allowed them to separate, revealing the stitching or binding underneath.