Short fiction types
A novel is usually considered to be 50,000 words or more. Less than that is considered short fiction, which falls into a number of different categories..
Novella 20k – 50k words Shorter than a full novel, but long enough for all the usual types of narrative, including multiple character arcs, character development, sub-plots, and so on.
Novelette 7.5k – 20k words Shorter than a novella. Due to the length constraint, it's better to include fewer characters and sub-plots, and give more focus to the main arc.
Short story 1000 – 7500 words Enough space for one well developed story arc, and the growth and development of one or two characters.
Flash fiction 1000 words or less Short enough to be restricted to a single theme, event, or emotion. There's no real time for lengthy setups or resolutions. Short works are best started in medias res and ended sharply. A jarring, dissonant ending can be used to great effect here.
Microfiction 300 words or less A single scene, moment, or feeling. The tight limit means you may need to choose whether you elaborate on characters or plot. Every word counts. It's best to use evocative language or thought provoking ideas. Let the reader's mind fill in the gaps you're forced to leave.
Tootfic Needs to fit into the Mastodon format. 500 characters or less, including hashtags.
Twitfic Needs to fit into the Twitter format. 280 characters or less, including hashtags.
Six Word Story 6 words only Every word is valuable. Try to make sure each one serves a purpose. Avoid filler words or anything which can be picked up from context.
* Contractions usually count as more than one word. Ideally, you should write it out uncontracted to get the true word count. But, you know, poetic license...