Technically part of the intake system. A diverter valve redirects turbo backpressure to the intake side of the turbo. This accomplishes two things, 1) does not damage turbo, 2) re-uses boost. A Diverter Valve is not to be confused with a Blow Off Valve or BOV which releases excess boost into the atmosphere while making the famous ‘Fast and the Furious’ “PSSSH” sound. Many say this sound can be somewhat replicated with an aftermarket or custom intake and a good diverter valve.
A diverter valve can also be called a “dv”, “divert air valve”, “bypass valve”, or “dump valve”.