“Prose” is the name for a kind of notational style. It’s a way of making language look responsible. You’ve got justified margins, capital letters to begin graphemic strings which, when they are concluded by periods, are called sentences, indented sentences that mark off blocks of sentences that you call paragraphs. This notational apparatus is intended to add probity to that wildly irresponsible, occasionally illuminating and usually playful system called language. Novels may be written in “prose;” but in the beginning no books were written in prose, they were printed in prose, because “prose” conveys an illusion of a commonsensical logical order. It’s as appropriate to the novel as ketchup to a hamburger, which is to say, it’s not very good but the hamburger wouldn’t go far without it.