Rat Rod is a new term... back in the day they were simply called "Hot Rods". My grandfather used to race on dry lake beds in California and he says that the rat rod term is something new cause his rusted 32 Ford was simply a "hot rod".
I found this on a bulletin board a while back and liked it so much I kept the quote:
"Rat Rod... Product of a fertile mind, empty pockets, recycled parts and desire to ride!"
A good definition of all the rod era vehicles can be read at:
www.honolulustreetsmagazine.com/autoshop.html