back story
From Longman Dictionary of Contemporary Englishback storyˈback ˌstory noun [countable] the things that happened to a character in a book or film before the beginning of the story being told in the book or film The back story of why she hates her father is a bit too contrived.Examples from the Corpusback story• His scripts are full of little gems, repeated phrases, unexplained back story and odd rhythms.