Complex and irregular waveforms:

The shape of an alternating current wave can get exceedingly complicated, but as long as it has a definite period, and as long as polarity keeps switching between positive and negative, it is ac.

Figure given below shows an example of the complex alternating current wave. You can see that there is a period, and thus a definable frequency. The period is the time between 2 points on succeeding wave repetitions.

With some waves, it can be difficult to tell the period. This is because the wave has 2 or more components which are nearly the same magnitude. When this happens, the frequency spectrum of wave will be multifaceted. The energy is split up among the two or more frequencies.

Figure--   An irregular waveform.