effects pedal

A foot-operated device, typically used by players of electric guitar (but in fact usable by any musical instrument or device with an audio output), plugged into the signal path between the instrument and the amplifier in order to alter the properties of emanating sound.

Single effects pedals can be of various types including chorus, reverb, overdrive, distortion, wah-wah, pitch-shift and so on. It is common to see several effects pedals linked in series on a live stage, often grouped onto a pedal board, where they can be toggled in any combination. Multi-effects pedals combine many of these together into the same box.