To overthrow; to annul; to make void or declare invalid; e.g., "quash a subpoena."
Unreasonable, obviously irregular, or oppressive subpoenas, injunctions, indictments, and orders can be quashed by a court. For example, if jurors have been selected improperly, the court can quash the proceedings.
In criminal cases, if an indictment is defective to such a degree that no judgment could be made if the defendant were to be convicted, the court typically will quash the indictment. In criminal cases, a motion made by the prosecution to quash an indictment is much more likely to succeed than one made by the defense, whose motion would appear self-serving.