- A frequency that resonates in response to a fundamental (primary) frequency. Sometimes, when a certain frequency is generated (a fundamental), it will also cause another frequency or frequencies to start as well. These are called harmonics. Source: Church Audio & Acoustics Glossary
- Sinusoidal quantity that has a frequency which is an integral multiple of the fundamental. Source: Glossary of Terms in Noise Control Engineering
- A higher-frequency signal related to a fundamental signal by some multiple.