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 every 100 females there are 94.9 males. For every 100 females age 18 and over, there are 92.0 males.
The median income for a household in the town is $69,819, and ...