the.com/dustjacket

means The removable paper cover wrapped around a hardback book, carrying the title, artwork, and blurbs while protecting the binding underneath.

from A plain compound of "dust" and "jacket" — a jacket being a covering or outer layer, the same garment-word that since the Middle Ages (via Old French "jaquet," a little tunic) has been borrowed to mean anything that sheaths something else: a potato's jacket, a boiler's jacket, a record's jacket. The "dust" simply names the job: a wrapper to keep grime off the cloth boards. Originally these covers were truly disposable — flimsy throwaways meant to be discarded once the book was shelved — which is exactly why surviving early ones are now prized.