Which of the following is defined as material that is not structured in a regular meter like poetry?

The choice of prose is accurate because prose refers to written or spoken language that follows a natural flow of speech, rather than a structured form characteristic of poetry. Unlike poetry, which often utilizes meter, rhyme schemes, and specific line breaks, prose is organized into sentences and paragraphs without a formal pattern. This makes it the primary mode of writing used in novels, essays, and short stories, where ideas are expressed in a straightforward, narrative manner.

The characteristics of prose are what distinguish it from the other options, such as essays, which can be written in prose but are not defined by their structure. Verse, on the other hand, specifically refers to poetic forms that are often rhythmical and structured. A stanza, similarly, is a component of a poem, consisting of a specific number of lines arranged in a recurring pattern. Thus, prose stands out as the form that eschews metrical structure, aligning directly with the definition provided in the question.