Other forms: backstories
A backstory is a specific history that led up to the current situation. If your parents come home to find popcorn all over the house and the dog wearing a tutu, they'll probably want to know the backstory.
Past events and circumstances that contribute to whatever's happening now can be called the backstory, in real life and also in fiction. Sometimes the backstory is spelled out for you, like a book character's lonely childhood that helps explain their difficulty connecting with people as an adult. Film actors sometimes invent a backstory for their roles, to help them understand why they behave the way they do. Backstory is a shortened version of "background story."