The number of vibrations per second of a musical pitch, usually measured in Hertz (Hz) .the number of wave crests per second, hertz.<br><br>The number of oscillations or cycles per unit of time. Acoustical frequency is usually expressed in units of Hertz (Hz) where one Hz is equal to one cycle per second.<br><br>The number of cycles of a waveform occurring in a second. In the sound world, we measure the number of sound vibrations per second, and give the result in cycles-per-second, or Hertz (Hz). The frequency is directly related to pitch and inversely related to wavelength.