Prose is generally characterized by syntax, or sentence structure. Sentences possess a subject and a predicate; these are frequently found in the order: subject (noun), verb, object (if applicable).
Poetry, however, may omit a subject or verb because it conveys ideas through a mixture of sounds and images rather than pure narration. Writing complete sentences is therefore unnecessary in poetry but typically required in prose.
Cormac McCarthy's The Road is littered with sentence fragments, descriptive phrases that fail to include a verb, or one word statements. For instance, the landscape is described on page 2 as "Barren, silent, godless." This sentence provides a series of adjectives, but fails to mention a noun. The effect, heightened by the use of asyndenton (the omission of the conjunction), promotes the notion that McCarthy's novel reads more like a poem, which is interested in conveying meaning through imagery, rather than prose, which uses direct story-telling.