Cross flow refers to the waters path through the radiator, to the tanks. Water takes the path of least resistance, so staggering the intake port & return ports on different sides of the tanks(crossflow), makes the radiator more efficent, or in the example of the origional style rads( intake & return on the same side) less efficent.
Sometimes crossflow is used to describe rads with the tanks on each side, hense cross flow, as the Fox body rad is. Though the ports are still staggered.