Fundamental frequency is the lowest frequency of a periodic waveform, representing the primary pitch of a sound. It is measured in Hertz (Hz) and determines how high or low a sound is perceived. For example, when a musical instrument like a guitar is played, the fundamental frequency is the main note that you hear. In addition to the fundamental frequency, there are also overtones or harmonics, which are higher frequencies that occur at integer multiples of the fundamental frequency. Together, these frequencies create the unique timbre or quality of a sound, allowing us to distinguish between different instruments or voices, such as a piano and a violin.