The short story is a form of narrative prose writing that is characterised by the number of words contained therein.
Determining the actual length of a short story is problematic. A classic definition of a short story's length is that it must be able to be read in one sitting. In contemporary usage, the term most often refers to a work of fiction no longer than 20,000 words (at one extreme) and no shorter than 1,000. (The definition of micro-fiction , which compresses the short story even farther, ranges in length but almost never exceeds 1,000 words.) But, in practice, a short story's length is determined by where it is published. Short stories can be found in print or online magazines, in collections organised by author or theme, and on blogs.
Short stories are most often a form of fiction writing. The most widely published form of short stories are genre fiction: science fiction, horror fiction, detective fiction, etc. The short story has also come to embrace forms of non-fiction such as travel writing, prose poetry and postmodern variants of fiction and non-fiction such as ficto-criticism or new journalism. Fiction which surpasses the parameters of the short story is called a novelettes or novellas–that underexplored territory between the short story and the novel. An extreme genre of short fiction is the 100-word drabble.
Geoffrey Chaucer's The Canterbury Tales, wrote a collection of tales in verse something close to short stories, influenced by books like the Decameron. And folk tradition from the beginning of time have contained some narratives that we might consider short stories (for example, Little Red Riding Hood.) Once printing was invented, writers were free to experiment with short prose translations of classic authors, and original fiction.
But a direct genesis of the modern short story is in the anecdote, the fictional Sir Roger de Coverley's letters relate: the character reappears through some of Addison and Steele's essays in the early 18th century. The anecdotes had the function of a parable, a brief realistic narration that embodied a point.
Addison and Steele's essays were published weekly, and the short story remained in part a creation of journalism. Magazines are still the venue of the modern short story. St. Nicholas Magazine was an early venue for the tales of Washington Irving for example. Nathaniel Hawthorne, Edgar Allan Poe, Herman Melville, and others like them created these brief tales because they fit nicely amongst the advertisements and the recipes, and the genre gelled in French with the atmospheric short stories of Guy de Maupassant.
The desire to tell a short tale in prose may stem from its resemblance to the writing of history, the sense of authority and verisimiltude that prose uniquely confers. Due to its origins in historical writing, prose can command weight and import . It is a form that forces you into a one-on-one connection with the author in a private setting. It demands a kind of attention and commitment that oral poetry typically can't match. Certainly our old chronicler decided that what he had was good enough for a chronicle, but not worth the time for a poem. He may even have preferred his stodgy, literate prose form to the florid oral poetry of his day. But certainly into modern times, those aesthetic concerns were bolstered substantially by the fact that magazines didn't have room for whole novels. Nor did they have as much use for poetry which seems to waste all of that perfectly good paper with a lot of white space.
Thus the modern short story was born from a combination of aesthetics and economics.
Its concerns remain very much the same now as they were a thousand years ago. There is a kind of austerity to the prose short story. It's no accident that Edgar Allan Poe used this form to invent the detective story. There is no better form to mimic the cold, clear style of a police report or a newspaper account. And it's no wonder that newspaper man Ernest Hemingway picked up the form one hundred years after Poe.
Certainly the form has many practitioners and many styles. These days especially, it traipses about the range of possible styles and genres, flirting with all sorts of poetic abstractions and excesses. Nonetheless, what was true a thousand years ago is still true today: the short story is a quick form set for quick action. Ephemerality dominates over longevity. There is no space, nor desire, for the weighty and lengthy examinations of the novel or epic poem. Only quick truths need apply: epiphanies, surprises, twist endings and suicides. Novels are divine because they, like gods, go on forever. But short stories are the perfect mirror of mortal man.