Backstory

A backstory, background story, back-story or background is the literary device of a narrative history and set of facts and factors all chronologically earlier than, and related to, a narrative of primary interest. Generally, it is the history of characters or other elements that underlie the situation existing at the main narrative's start. Typically, the genres in which a backstory may be revealed include all entertainment media being significant in all literary works such as novels or short stories, stage or radio plays, and so also derivative media such as TV dramas and movie films. Even a purely historical work selectively reveals backstory to the audience, a backstory which may receive alternative creative emphasis in each rendition of a novel, play, or film, while each shares key elements—however differently they may be depicted and revealed—which are factors of timing, style and story telling art of a given media while the whole of a backstory goes to facts.

Read more about Backstory:  Usage, Recollection, Shared Universe