backtracking vs footstep

backtracking

noun
  • The act of one who, or that which, backtracks; a retracing of one's steps. 

  • The usage of a runway as a taxiway, especially at private strips and smaller airports. 

  • The act of building all possible solutions to a problem incrementally, abandoning any candidate solution if it cannot lead to a valid solution. 

footstep

noun
  • The act of taking a step. 

  • A step, as in a stair. 

  • The sound made by walking, running etc. 

  • The mark or impression left by a foot; a track. 

  • The distance between one foot and the next when walking; a pace. 

  • The indications or waypoints of a course or direction taken. 

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