To set aside.
To set aside; to rescind; to vacate; to render null and void.
To quash a conviction means to set it aside as if it never existed.
A motion to quash seeks to rescind a previous decision or a document or decision.
If a subpoena is issued improperly, a motion might be presented to the Court to quash the subpoena.
A certiorari application may request of the Court that the lower tribunal's decision be quashed.