Georgia Overdrive is tranny in neutral and let gravity have its way.
Why Georgia?
Because Georgia was (is) considered poor and unsophisticated and unlikely to have such advanced things a "overdrive" on their vehicles.In the same way, a piece of cardboard over the radiator in the winter is called a Georgia Thermostat.
Spaw is quite correct; it is a very dangerous and stupid manouver with a big rig and is equally dumb with a smaller vehicle.
Except SUV's. They can do it all they want to.Heh,heh,heh.

troll