“Fiction is any narrative, especially in prose, about invented or imagined characters and action. Today, we tend to divide it into [four] major subgenres based on length—the [short short story], short story, novella, and novel. Older, originally oral forms of short fiction include the fable, legend, parable, and tale. Works may also be categorized not by their length but by their handling of particular elements such as plot and character….” (The Norton Anthology of World Literature: Literary Terms)
Novel — Over 70,000 words
Novella — 17,500 to 70,000 words
Novelette — 7,500 to 17,500 words
Short Story — 1,000 to 7,500 words
Short Short Story — Under 1,000 words
Microfiction — Generally, 500 words or less (Some editors will consider everything 1,000 words or less to be a short short story or flash fiction. Some editors will consider a microfiction to be 100 words or less. There is a great deal of variance between editors. If in doubt, simply ask the particular editor.)
Novel: a long work of fiction, typically published (or at least publishable) as a standalone book; though most novels are written in prose, those written as poetry are called verse novels. A novel (as opposed to a short story) conventionally has a complex plot and, often, at least one subplot, as well as a fully realized setting and a relatively large number of characters. One important novelistic subgenre is the epistolary novel—a novel composed entirely of letters written by its characters. Another is the bildungsroman.novellaa work of prose fiction that falls somewhere in between a short story and a novel in terms of length, scope, and complexity.
Novella: it can be, and has been, published either as a book in its own right or as part of a book that includes other works. Franz Kafka’s The Metamorphosis is an example.
[Novelette: Shorter than a novella, longer than a short story.]
Short Story: a relatively short work of prose fiction that, according to Edgar Allan Poe, can be read in a single sitting of two hours or less and works to create “a single effect.” Two types of short story are the initiation story and the short short story. (Also sometimes called microfiction, a short short story is, as its name suggests, a short story that is especially brief; examples include Linda Brewer’s “20/20” and Jamaica Kincaid’s “Girl.”)
[Short Short Story: a short story that is approximately 1,000 words or less. Often, expositional attributes are cut or shortened.]
[Microfiction: a short story that is approximately less than 500 words. Often expositional attributes are cut or shortened. Time lapses will be briefer and the reader will be asked to invest far more imaginative response. Micro fictions are often close to poetry and can sometimes be interchangeable with prose poetry.]
A Handbook to Literature. William Harmon.
The Norton Anthology of World Literature: Literary Terms. Martin Puchner, et al.
Writing Fiction: A Guide to Narrative Craft. Janet Burroway, Elizabeth Stuckey-French & Ned Stuckey-French.