1) Literary technique 
A backstory, background story, back-story or background is a set of events invented for a plot, presented as preceding and leading up to that plot. It is a literary device of a narrative history all chronologically earlier than the narrative of primary interest. Generally, it is the history of characters or other elements{which | date=July 2013} t...
The history behind characters and events, often included as flashbacks or slipped into the dialogues or recollections of the characters.
Information about past events or thoughts that shaped the characters or story world.