back matter vs postlude

back matter

noun
  • The parts of a book that appear after the main portion of the body text, including the afterword, index and bibliography; the end matter. 

postlude

noun
  • A concluding passage of text or speech; an epilogue or afterword. 

  • The final part of a piece; especially music played (normally on the organ) at the end of a church service. 

verb
  • To form a postlude (to); to end with a postlude. 

How often have the words back matter and postlude occurred in a corpus of books? (source: Google Ngram Viewer )