Form is a way of categorizing literature based on its structure or purpose. One way of using the term genre is to refer to formal genres, a way of classifying literary works by their form.
"When we speak of the form of a literary work we refer to its shape and structure and to the manner in which it is made - as opposed to its substance or what it is about. [...] A secondary meaning of form is the kind of work - the genre to which it belongs. Thus: sonnet, short story, essay."
-J.A. Cuddon and M.A.R. Habib, The Penguin Dictionary of Literary Terms and Literary Theory, "Form"
According to J.A. Cuddon and M.A.R. Habbib (The Penguin Dictionary of Literary Terms and Literary Theory, "novel"), the term novel is
derived from Italian novella, 'tale, piece of news', and now applied to a wide variety of writings whose only common attribute is that they are extended pieces of prose fiction. [...] It would probably be generally agreed that, in contemporary practice, a novel will be between 60,000 words and, say, 200,000. [...] We may hazard it is a form of story or prose narrative containing characters, action and incident, and, perhaps, a plot. [...] The subject matter of the novel eludes classification. No other literary form has proved so pliable and adaptable to a seemingly endless variety of topics and themes.
Cuddon and Habbib go on to summarize the history of the novel form, but more extensive treatments of the history of the novel in general and in particular Anglophone literatures can be found in the boxes below.
A short story, according to J.A. Cuddon and M.A.R. Habbib, is "a prose narrative of indeterminate length, but too short to be published separately as novels or novellas usually are. According to Edgar Allan Poe, it is a story that concentrated on a unique or single effect and one in which the totality of effect is the objective."
Short fiction is a term that encompass not only short stories but typically longer forms such as novellas and novelettes, as well as short-short forms such as flash fiction.
Short stories tend to be published in periodicals as well as short story anthologies. Anthologies range from stories by multiple authors selected for a particular theme, to collections of the best stories from a given time or place, to anthologies which collect the entirety or a selection of an author's short fiction.