Double-clutching (technique)

Double-clutching (also called double de-clutching outside of the United States) is a method of shifting gears used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. While double clutching is not necessary in a vehicle that has a synchronized manual transmission, the technique can be advantageous for smoothly downshifting in order to accelerate and, when done correctly, it reduces wear on the synchronizers, which act to equalize transmission input and output speeds to allow downshifting.

Source: Wikipedia — Double-clutching (technique) (CC BY-SA 4.0)