What does the "total harmonic distortion" mean?

The total harmonic distortion describes a value that tells you how much headphones distort sound under certain conditions. This is measured in relation to the original signal, which is why the value is specified as a percentage. As distortion negatively affects the transmission quality, headphones with a high total harmonic distortion sound unclear and, in the worst case, even annoying, which is why it is best to have the lowest total harmonic distortion possible.