What is the difference between Upfitting and Refitting Fleet Vehicles?

If you went to the dealer and bought a "cab chassis"--just the frame rails sticking out behind the cab--then took it to Dixie Upfitting and had it turned into a refrigerated box van, it would have been upfitted. If you went to the same dealer, bought a used dump truck, then took that truck to Dixie Upfitting and had it turned into a refrigerated box truck, it would have been refitted.