Definition of backward masking in English:

backward masking

noun

  • 1Psychology
    Psychology the alteration or diminution of the perception of a (visual or auditory) stimulus by a second stimulus which follows it closely; compare metacontrast.

    See also metacontrast
  • 2The inclusion of a message in a piece of recorded music which can be understood if the music is played backwards, and which is said by some to have a subliminal effect when the music is played normally.

Origin

1950s; earliest use found in Journal of the Acoustical Society of America.