Apart from its length, what else makes a short story different from a novel?
A short story can employ first-person point of view; a novel, because of its complexity, cannot.
A short story normally does not have a complicated plot; a novel can have a complicated plot.
A short story does not have the five phases in a plot diagram; only a novel does.
A short story’s characters face many small conflicts; a novel's characters deal only with large conflicts.