"Yard tractor, yard buggy, hostler, shifter, piece o chit". Whatever you wanna call it, it's those white or, used to be, yellow half-cabs that run around the yard and sometimes cross city or county streets (if they're licensed). Can raise 5th wheel more than a foot above normal so they don't hafta get out and crank legs up and down each time for hundreds of moves each day or night.