It refers to a feature in vehicles with automatic transmission that allows the transmission to suddenly shift to a lower gear when the driver quickly depresses the accelerator pedal. This is used to maximize vehicle acceleration and momentarily provide more power to the driver. Kickdown is especially useful when overtaking, when sudden acceleration is required or when going uphill.
In some cases, this feature may be cumbersome and the driver may not want it. This feature can be removed with this module.