Here's a breakdown:

* Fundamental frequency: The lowest frequency in a sound wave, often referred to as the "first harmonic."

* Harmonics: Frequencies that are whole-number multiples of the fundamental frequency. For example, the second harmonic is twice the fundamental frequency, the third harmonic is three times the fundamental frequency, and so on.

The combination of the fundamental frequency and its harmonics creates the unique sound quality, or timbre, of a musical instrument or voice.