What is double clutching?

My kid asked and I don't know. (doah!)

pushing the clutch in when shifting out of gear letting off and pushing it in again to put it into gear, its a timing thing for some people.... Truckers do it alot....

usually done if you dont have fully synchronised gears'''like into first on some cars

Also done at 55 MPH between 3rd and 4th gear, so you can let the Mustang 5.0 on your right know you have another gear left and he's all out. I've done it a few times with success, revving the engine coming out of third gear so it lurches into 4th. :p