A short story, as the name implies, is shorter in length than a novel. Short stories are usually fewer than 10,000 words, while a novel is normally 60,000 to 100,000 words or more.
This difference in length influences the other aspects of the genres. A short story has a simpler plot than a novel. It usually focuses on only one or two characters and often on a single episode in an individual's life or on the quick summary of a life. The setting is simpler, usually focusing on one or two places, whereas in novels, multiple locations are usually involved.
A key difference between novels and short stories is the ability to develop characters more fully in the novel. A short story will focus on one or two character traits in a protagonist. It will often summarize aspects of a person's character rather than developing them through showing the character interacting with others. A novel offers the possibility of exploring more than one fully rounded character, whose strengths and weaknesses can be minutely examined. It also allows for the possibility of creating a whole world of characters of different types and classes who can interact with each other and represent different points of views.
In summary, the length of a novel allows for more complexity, while a short story usually makes a single point.