A Tritone is a Sharp Fourth (#4) or Flat Fifth (b5) of a scale. Commonly used in music to create a smooth/cool sound (As in the blues.) or to create a brooding and/or mysterious atmosphere (Common in rock and metal playing.). A good example of Tritone use can be found in the Black Sabbath song "Black Sabbath.". The Black Sabbath guitarist, Tony Iommi is known for pionereing of the tritone to create heavy riffs. He learned to apply this after playing a series of notes, creating a tune that had his "Hair standing on end.".