a) Whole number multiples of a frequency. F x 1 is called the fundamental or first harmonic; F x 2 is the second harmonic; F x 3 is the third harmonic; etc. b) Integral multiples of a fundamental frequency are harmonics of that frequency. A pure sine wave is free of harmonics.

Adding harmonics to a fundamental frequency will change its wave shape.

A square wave contains a fundamental frequency plus all the odd harmonics of that frequency.