The EHX Performance Series Expression Pedal by Electro-Harmonix is designed to provide external control over applicable effects. Say you have a flanger pedal whose speed parameter can be controlled by an expression pedal; if that were the case, you could use this Electro-Harmonix product to control that parameter.
The EHX Expression Pedal sports a single 1/4" TRS output, as well as a range knob that allows you to tune the width of the pedal's sweep; this way you can vacillate between narrower values using the entirety of the pedal's rocker and affect a more granular sweep, if you so choose. A polarity reverse button is on hand to ensure compatibility with other pedals made by many different manufacturers, while a reverse button lets you change the direction of the sweep.
The pedal has been constructed out of polymer, thus offering stability on the road. A 6' TRS cable is included for use with the pedal.