Answer: Saddle Stitching
Aw, that was an easy one 😉 Saddle stitching gets its name from the equipment used to perform this binding method. Your printed sheets are folded to form a booklet, which is then draped over the part of the machine that resembles a saddle. They are then stitched together along the crease of the fold.
The “stitches” are most commonly done with wire that looks like a staple. In the image above, though, the binding is truly stitched with thread – a manual task!