backstory vs work of fiction

backstory

noun
  • A fictitious account of a person's history designed to conceal their actual history and motives. 

  • The previous life and experiences of a person, especially a character in a dramatic work, but also a real-life person. 

  • A prequel. 

work of fiction

noun
  • A fictitious account; an account of events that never took place. 

  • A fictional account; a story. 

How often have the words backstory and work of fiction occurred in a corpus of books? (source: Google Ngram Viewer )