What bookdealers really mean. A dictionary by Tom Congalton and Dan Gregory (Between the Covers), with additions from other sources
Refers to the condition of a book; the wrinkled, puckered, waving, or curling condition of a page or of the boards of a book, which is caused by non-uniform drying and shrinkage. If the cockled page is made of vellum, the condition is caused by humidity. In the case of paper or board, the condition is caused by heat and humidity. In the case of book covers, it can be caused by the use of the wrong type of adhesive or too much adhesive.