This is the process of using a specially designed ecu map, to give different power outputs with maf (air flow mass sensor) connected and disconnected.  The usual scenerio would be to use the maf connected for a lower power/economy map, and maf disconnected to give a all out power map.  This is a very handy tool for taking the strain off particular components, and giving the extra power when needed.  At the present moment this can only be achieved on the older 25/45/ZR/ZS obd1 compliant cars.