The Supra Turbo comes equipped with an air bypass valve for turbo protection.  These allow excessive turbo pressure to returned to the intake system when the throttle plate is closed.  A bypass valve, as defined by this site, is a valve that allows the turbo pressure to be routed back to the intake stream similar to the OEM part.  These are the types you would want to use without having to worry about problems associated with the stock Air Flow Meter.  A blow off valve is defined as the valve that allows the pressure to vent to atmosphere, or "blow off" the pressure.

Bypass Valve                                   Blow Off Valve