forum vs piazza

forum

noun
  • A square or marketplace in a Roman town, used for public business and commerce. 

  • A gathering for the purpose of discussion. 

  • A place for discussion. 

  • An Internet message board where users can post messages regarding one or more topics of discussion. 

  • A form of discussion involving a panel of presenters and often participation by members of the audience. 

piazza

noun
  • A public square, especially in Italian cities. 

  • A roofed gallery or arcade (for example around a public square or in front of a building). 

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