EXPRESSIONPEDAL
Expression pedal
An expression pedal is an important control found on many musical instruments including organs, electronic keyboards and pedal steel guitar. The musician uses the pedal to control different aspects of the sound, commonly volume. Separate expression pedals can often be added to a guitar amplifier or effects unit and used to control many different aspects of the tone.The above text is a snippet from Wikipedia: Expression pedal
and as such is available under the Creative Commons Attribution/Share-Alike License.