prep school vs university

prep school

noun
  • A private primary school which prepares its pupils for the common entrance examination most commonly at the age of thirteen, and subsequent entry into public school. 

  • A private or public school intended to prepare its students to get into prestigious universities. 

university

noun
  • Institution of higher education (typically accepting students from the age of about 17 or 18, depending on country, but in some exceptional cases able to take younger students) where subjects are studied and researched in depth and degrees are offered. 

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