Chorus

From GuitarWiki

A chorus effect is a mixture of a delayed sound and the original sound, the delayed sound is delayed by approximately 20ms. The shimmering effect of a chorus pedal is created by varying the time delay by plus or minus 5 milliseconds, the listener would then here a slight pitch variations. Each chorus device comes with a rate and depth control, the depth control varies the amount by which the pitch fluctuates and the rate controls various how quickly the pitch fluctuates. Sometimes a feedback control is also added to send the delayed signal back to be delayed again and this can intensify the effect.

The chorus effect is best used on a clean guitar signal as adding chorus to a distorted guitar signal can muddy your tone and adds a perceptions of spaciousness to the sound.

A chorus effect can be included within a foot pedal (eg. Boss CE-3), rack-mounted effects bank or even built-in with an amplifier.