A back-story is a literary device[?] often employed in order to lend a story depth or verisimilitude. Characters or events related to a story may only be given cursory treatment so as not to distract from the central plot development.
Probably the most extensive back-story ever created was that created by J. R. R. Tolkien for his Middle-earth stories.
... for a family is $74,412. Males have a median income of $55,625 versus $33,000 for females. The per capita income for the village is $38,500. 9.0% of the population and ...