folding money vs paper money

folding money

noun
  • Paper currency; cash in the form of printed banknotes. 

paper money

noun
  • Cash in the form of banknotes. 

  • A type of joss paper resembling banknotes burnt to venerate the deceased, ancestor spirits, deities, etc. 

How often have the words folding money and paper money occurred in a corpus of books? (source: Google Ngram Viewer )