What is Back-story?
1.
The history of the story. How the story became news. The rest of the story.
I've heard this used on CNN a couple of times. "Back story" is used when talking about a breaking news story, when the rest of the story isn't clear. "What is the back-story on the train crash?" Meaning how many were on the train. When did it leave, and how fast was it going?
See