Harmonic distortion occurs when a signal is altered, creating additional frequencies that are multiples of the original frequency. This can happen in audio systems, where the sound produced may not accurately represent the intended signal. The result is a change in the quality of the sound, which can lead to a less clear or distorted output. In electronics, harmonic distortion is often measured as a percentage, indicating how much of the output signal is made up of these unwanted harmonics. Devices like amplifiers and speakers are designed to minimize harmonic distortion to ensure high-fidelity sound reproduction, preserving the integrity of the original audio signal.