intro vs lead-in

intro

noun
  • An introduction. 

  • The opening sequence at beginning of a film, television program, etc. 

  • A small demo produced to promote one's demogroup or for a competition. 

verb
  • To introduce. 

lead-in

noun
  • An introduction; something that leads into the beginning of something. 

  • A short phrase that begins the caption of a photograph. 

  • A region of data at the beginning of a compact disc, holding the table of contents. 

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