Related Information
Image source: Endpapers of ABC for Book Collectors, John Carter & Nicolas Barker (Oak Knoll Press, 2004) 8th Edition.
Hinge
the inside portion of the flexible area where book cover meets the book spine; often used interchangeably with the term joint, which should be used to designate the outside or exterior portion of the "hinge". A volume which has received heavy or rough use often has cracked or broken hinges.