People have a tendency to classify things--animals get tagged and sorted by biologists, languages are divvied up in philogy, geologists spend their days stratifying the earth. Stories, it seems, are no exception.
In fiction, most folks have a ready understanding of what a novel is. On the surface, it might be a thick tome in leather binding or a pulp paperback sitting in a spinner rack, but everyone knows what's going to be inside the covers. A lengthy story with protagonists, antagonists, rising and falling action, a subplot or two, that's going to take the typical reader a few sittings to get through.
But there's a range of shorter fiction writing out there, works that don't run the length of a novel. Over time, there has come to be a commonly recognized delineation between different kinds of shorter fiction based on word count. So we have the ...
Novella: 17,500 – 40,000 words
Novelette: 7,700 – 17,500 words
Short Story: Less than 7,500 words
(* You could add to this list, "flash fiction," which is a short story under 1,000 words)
Most people have a pretty good intuitive idea of what a short story is. It's a piece of fiction that you can sit down and read in one sitting. Usually it will entail no more than 3 or 4 scenes. Rarely will a short story venture far from a primary character (it's a hard trick switching point of view between multiple characters with only a 7,500-word runway). But novellas and novelettes aren't terms that are frequently used outside of writing circles.
Here is what Jericho Writers says about the novella and novelette:
Novellas tend to follow a linear structure with the main action centred on the protagonist's development. This could be an inner conflict that is resolved or simply explored, rather than a series of events. Due to brevity, there isn't the scope for several sub-plots or settings although some elements of the novel may have some complexity.
If the novella is the younger sibling of the novel, then the novelette falls somewhere in between a short story and a novella.
With a word count of around 7,500-19,000 words, the novelette borders both the top end of a short story and the length usually acceptable for a novella. As with the short story and the novella, writers may be constricted in terms of the number of characters they can use and the amount of plot development they can include.
The plot will probably be linear and uncomplicated with few, or no, sub-plots. One or two characters will feature – not a cast of hundreds. It will have a defined focus and will be complete as a story. The novelette enables writers to give more flesh to the bones of their short story, though the writing still needs to be concise.
I've found novelettes and novellas an enjoyable pastime for fiction writing. In fact, that's been my focus lately. Look With Your Eyes was my first published novella. I've had a couple of novelettes included in short story mags. True, these kind of stories don't enjoy the popularity they used to (although trends can always change), but they're so much fun to write. You can experiment, work with off-the-wall ideas you'd never sink into a full-blown novel, because there's not nearly the same time commitment. The focused attention these forms demand is good for me (you can't chase rabbits down holes when you're limited to 50 or 60 manuscript pages).
Stories have always come in all sorts of shapes and sizes. Today we have some handy labels to keep track of them.