A form of narrative fiction, the short story has characters and plot, just like a novel, but it's, you know, shorter. Wow, we really just rocked your world, huh?
Short stories resemble other short form genres like apologue and fable, but the genre really took off in the 19th century with peeps like Edgar Allan Poe and Anton Chekhov.
The short story really took off in 20th century and beyond. Most writers of literary fiction today have at least dabbled in them, if not dived in whole hog, like an awesome lady named Alice Munro, who writes almost exclusively in the form.