What is the hose that goes from overflow to bottom of rad on a 2002 windstar?

That hose is called the overflow hose or sometimes the radiator overflow hose. While it connects the overflow tank to the radiator, it's more accurate to say it goes *from* the radiator's overflow neck *to* the overflow tank, rather than the other way around. Coolant flows *into* the overflow tank when the system is pressurized, and then back *into* the radiator when the pressure drops.