In my book, all tales and tellings are stories, some longer than others. I think the way we categorize them is somewhat arbitrary.
However, people who ponder this more than I do seem to agree that the short story can be read in one sitting; and that it usually concerns only one protagonist, and often consist of only one—longer or shorter—scene.
As a story it may or may not resolve (the way we want novels to resolve); and the short story is often a sample of what some call a slice of life.
Anton Chekhov is considered the father of the modern short story, and for good reason. Reading him, even in translation—where so much comes down to the skills (both lingual and fictional) of the translator—is like savoring something holy.
The current master of the short story, at least in my view, is Mavis Gallant.
I have written two scores—perhaps closer to fifty, by now—of these tales, but I have published only a few of them, some individually, and some in two collections.
Happy—and, I hope, rewarding—reading.
Ulf Wolf