courtyard vs terracing

courtyard

noun
  • An area, open to the sky, partially or wholly surrounded by walls or buildings. 

terracing

noun
  • A terraced structure. 

  • A series of terraces. 

  • A stand with a series of tiers. 

  • The formation of terraces. 

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