noun (n)

• the act of concealing the existence of something by obstructing the view of it(noun.act)

  Synonym:
  cover, covering, screening
  

  source: wordnet30
• the blocking of one sensation resulting from the presence of another sensation(noun.cognition)

  Example:
  He studied auditory masking by pure tones.
  

  source: wordnet30
• scenery used to block the audience's view of parts of the stage that should not be seen(noun.artifact)

  Synonym:
  masking piece
  

  source: wordnet30