Stereo refers to a sound setup or effect that uses two channels (left and right) to create a sense of space and dimension in the audio. In a stereo configuration, sounds are panned across the left and right speakers or headphones, providing a more immersive and dynamic listening experience compared to mono, which uses only a single channel.

In the context of guitar pedals, a stereo pedal can output a signal to two separate channels, offering a broader soundstage and enhancing effects like delay, reverb, chorus, and panning. This allows for more complex and expansive soundscapes, with some pedals offering true stereo outputs to achieve rich, spatial effects that evolve across both channels. Popular stereo pedals include the Strymon Timeline, Eventide H9, and Electro-Harmonix Holy Grail Stereo, which all utilise stereo outputs to create rich, evolving tones that feel more immersive in a performance or recording setting.