What bookdealers really mean. A dictionary by Tom Congalton and Dan Gregory (Between the Covers), with additions from other sources
As in: "separated at the rear spine fold." The crease or bend in the paper that is created when a jacket is bent around the edge of the spine – there are two of these, in case you wondered – a front spine fold and a rear spine fold. Spine folds create slight weakness in the paper that might eventually become the location of a tear or chip.