[aerohead]

The term is from Goro Tamai, and describes what happens when an otherwise smooth, 'flat', underbody is 'cambered' downwards, creating a crude venturi, in which the flow velocity is accelerated, and static pressure reduced, in opposition to the upper body's suction peak attempting to produce lift.
If properly 'tuned', it can cancel the upper body lift.
On a road vehicle, SAE 'breakover' clearances between the two axles would have to be respected, or the car could 'high-center' on driveway ramps and railroad crossings.