'Acid' is a sound typically produced by playing a repeating note pattern on the Roland TB-303 (or imitations of the 303), while altering the filter's cutoff frequency, resonance, and envelope modulation. The TB-303's accent control modifies a note's volume, filter resonance, and envelope modulation, allowing further variations in timbre. A distortion effect, either by using a guitar effects pedal or overdriving the input of an audio mixer, is commonly used to give the TB-303 a denser, noisier timbre–as the resulting sound is much richer in harmonics.

The sounds were originally developed by mid-1980s DJs from Chicago who experimented with the 303. The result spread to the United Kingdom, Australia, and continental Europe, where it was played by DJ's in the early rave scene. By the late 1980s, copycat tracks and acid house remixes brought the style into the mainstream, where it had some influence on pop and dance styles.

This tag is usually used for any music that employs this sound.