Overtones refer to the additional frequencies that are present in a sound beyond its fundamental frequency. Overtones are also sometimes referred to as harmonics or partials.
When a sound is produced, it typically contains a fundamental frequency, which is the perceived pitch of the sound. However, the sound also contains additional frequencies at higher multiples of the fundamental frequency, known as overtones or harmonics. These overtones give a sound its unique tonal character and can greatly affect its timbre.
In synthesis, overtones can be generated and shaped using various techniques, such as waveform selection, filtering, and modulation. By controlling the level and frequency of different overtones, users can create complex and expressive sounds that are unique to their particular synthesis setup.