What does this mean on this sites reviews?

[PolkFan]

Ok i know what it is now lol sorry its late but why is their distortion even when its barely in use? Very new to measurements.

 

[sergeauckland]

Those graphs don't just show distortion. The vertical axis shows THD+N, i.e. distortion plus noise. As the output level decreases, the noise however remains substantially constant, so the contribution from noise rises as a percentage as levels drop. At very low levels, the THD+N figure is pretty much only the 'N' part, whilst at high levels, the 'N' forms only a small part, and the THD is dominant. On a good item, the THD part is very small, which is why as output increases, the THD+N figure will decrease until the items starts clipping, at which point the THD part rises very rapidly.

S.