In comb binding a book, rectangular holes are punched through leaves, adjacent to the spine, and the "teeth" of a flexible plastic comb are passed through the holes so that the comb forms the spine. Typically, a manual or powered machine is used to punch the leaves, then insert the plastic comb. Combs are available in standardized sizes that can accommodate up to 425 leaves. Comb binding is an expedient method of binding that is low cost, requires minimal skill, and results in a book that will lie flat when open.
The first image shows an uncorrected proof copy, comb bound because the proof was considered impermanent compared to the trade edition. The second image shows a data handbook used in the selling of trucks.