“Deckle edge” (with quotes) are paper that, once bound, present a jagged fore edge, making the experience of running one’s fingers along the edge of the book a purgatory of paper cuts.
The explanation Amazon gives for why some books have “deckle edge” paper is as follows
So, “deckle edge” paper are a modern, machine-produced paper that’s made to resemble old/hand-made paper . Of course, we all know that when we buy a glossy jacketed book — the kind most likely to feature “deckle edge” — that it’s neither old nor handmade. Nobody will think that it’s either. Anybody who values old books or handmade papers surely knows what these products look like, and “deckle edge” is not going to fool them for a second. Why do we want to pretend that it’s old? Let’s not forget that old papers are deckled because of inferior technology that made it impossible for them to achieve the straight fore edge. “Decked edge” books are not old; they don’t look old; they look odd. Why do commercial publishers insist on producing them?