Total Harmonic Distortion (THD)
The percentage, in relation to a pure input signal, of harmonically derived frequencies introduced in the sound reproducing circuitry and hi-fi equipment, including speakers.

Treble (highs)
The upper end of the audio spectrum which is reproduced by tweeters.

Tweeter
A driver that is designed to reproduce the high or treble range of the sound spectrum.

Two-way
A type of speaker system composed of two distinct drivers, each dedicated to a different audio range.