How long is a short story, a novel, etc? I use the same definitions as the Science Fiction Writers of America (SFWA), but many people have their own personal definitions. I once came across a writer who wrote what I'd call short stories (around 7,000-8,000 words) and marketed them as novels, and I've also met epic fantasy novelists who consider anything less than 60,000 words to be a novella. Below are the definitions I use, including my personal definition for flash fiction (short short stories).
The SFWA definitions:
Novel—40,000 words or over
Novella—17,500 to 39,999 words
Novelette—7,500 to 17,499 words
Short story—under 7,500 words
Flash fiction—under 1,000 words
These are from fantasy, SF, and other writers.
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." Kurt Vonnegut Jr. (Breakfast of Champions)
"A short story is the nearest thing I know to lyric poetry...A novel actually requires far more logic and far more knowledge of circumstances, whereas a short story can have the sort of detachment from circumstances that lyric poetry has." William Faulkner
"Read poetry every day of your life. Poetry is good because it flexes muscles you don’t use often enough. Poetry expands the senses and keeps them in prime condition. It keeps you aware of your nose, your eye, your ear, your tongue, your hand.
And, above all, poetry is compacted metaphor or simile. Such metaphors, like Japanese paper flowers, may expand outward into gigantic shapes. Ideas lie everywhere through the poetry books, yet how rarely have I heard short story teachers recommending them for browsing.
What poetry? Any poetry that makes your hair stand up along your arms. Don’t force yourself too hard. Take it easy. Over the years you may catch up to, move even with, and pass T. S. Eliot on your way to other pastures. You say you don’t understand Dylan Thomas? Yes, but your ganglion does, and your secret wits, and all your unborn children. Read him, as you can read a horse with your eyes, set free and charging over an endless green meadow on a windy day." Ray Bradbury (Zen in the Art of Writing)
"Write a short story every week. It's not possible to write 52 bad short stories in a row." Ray Bradbury