noun (n)

• a noticeable deterioration in performance or quality(noun.process)

  Example:
  A drop-off in attendance.
  

  Synonym:
  falling off, falloff, slack, slump
  

  source: wordnet30
• a steep high face of rock(noun.object)

  Synonym:
  cliff, drop
  

  source: wordnet30
• a change downward(noun.event)

  Example:
  There was a sharp drop-off in sales.
  

  Synonym:
  decrease, lessening
  Antonym:
  increase
  

  source: wordnet30