in-joke vs parody

in-joke

noun
  • Synonym of inside joke (“a joke that is understood or meant to be understood only by certain people who are aware of the details”) 

parody

noun
  • A work or performance that imitates another work or performance with ridicule or irony. 

verb
  • To make a parody of something. 

How often have the words in-joke and parody occurred in a corpus of books? (source: Google Ngram Viewer )