essay vs pop quiz

essay

noun
  • A written composition of moderate length, exploring a particular issue or subject. 

  • A proposed design for a postage stamp or a banknote. 

verb
  • To move forth, as into battle. 

pop quiz

noun
  • A quiz or test given without warning or prior announcement. 

How often have the words essay and pop quiz occurred in a corpus of books? (source: Google Ngram Viewer )