Quash Definition:

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.