Harmonics
From MyMCAT
Harmonics
The harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. For example, if the frequency is f, the harmonics have frequency 2f, 3f, 4f, etc, as well as f itself. The harmonics have the property that they are all periodic at the signal frequency.
The harmonic with the longest period or the lowest frequency, is called the first harmonic. The harmonic with the second longest period is called the second harmonic and so on.
