Genres
Novella
Prose fiction longer than most short stories but shorter than most novels; award rules usually draw the lower line near 17,500 words.
A novella is a book of narrative prose fiction whose length is shorter than most novels but longer than most novelettes and short stories: fiction intermediate in length and complexity between a short story and a novel, as the Merriam-Webster definition the article cites puts it. There is no universal threshold; the Science Fiction and Fantasy Writers Association draws the line at 17,500 to 40,000 words. The word comes from the Italian novella, a short tale of true-seeming events, and the form flowered in early Renaissance Italy with Boccaccio's Decameron (1353). The canon includes The Old Man and the Sea, A Christmas Carol, The Metamorphosis, Animal Farm and Of Mice and Men. Structurally it sits between: fewer but more developed conflicts than a short story, fewer subplots than a novel, often readable in a single sitting.
Stephen King notes novellas are hard to sell commercially because they fit neither standard magazine nor book lengths, which is exactly the gap web publishing fills: a completed web serial arc has a natural home online. See how long is a novel for where the novel's own boundaries sit.