Circuit/System Description
WARNING: This page is about a different car, the 2019 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
The turbocharger bypass valve is a pressure relief valve in the intake system. It short-circuits the inlet and the outlet of the fresh air side of the turbocharger. This is used to maintain the rotational energy of the turbine when the throttle valve is quickly closed and the compressed air would have nowhere to go. The bypass valve allows the air to be pumped in circles which avoids pressure spikes.