What is narrative prose that brief in nature called?

There isn't one specific, universally accepted term for brief narrative prose. However, depending on the context and length, you could use several terms:

General terms:

* Short story: This is the most common term for a brief work of fictional narrative prose, typically ranging from a few hundred to several thousand words.

* Vignette: A short, evocative, and often descriptive piece of writing, focusing on a specific moment or scene.

* Sketch: A short, informal piece of writing, often experimental in nature, that explores a specific idea or theme.

* Anecdote: A brief, personal story about a specific event or experience.

* Parable: A short story with a moral lesson.

More specific terms:

* Flash fiction: Extremely short stories, typically only a few hundred words or less.

* Microfiction: Even shorter than flash fiction, often only a few sentences or even a single paragraph long.

* Drabbles: Stories exactly 100 words long.

* Six-word story: A story told in only six words.

The best term to use will depend on the specific piece of writing you are referring to and the context in which it is being used.