Distortion (dɪ̀stɔ́ršən) is commonly known as harmonic distortion, which is an effect created by clipping parts of the guitar signal, usually by an amplifier or an effect pedal. This clipping changes the shape of the waveform, thus changing the sound. Distortion (guitar) produces a sound with more sustain and more harmonic content; the sound is described as fuzzy or gritty.

Distortion (guitar) can be applied to either an electric guitar or any other instrument that produces electrical signal, such as an acoustic guitar with a saddle pickup. Distorted guitar tones gained popularity with the rise of rock and roll in the 1950s, and saw greatest use in the 1970s by bands such as Led Zeppelin and Pink Floyd, who used distortion to produce dirtier and fuzzy guitar sounds.