A motion to quash is a request to a court or other tribunal to render a previous decision or proceeding null or invalid.
The exact usage of motions to quash depend on the rules of the particular court or tribunal.
In some cases, motions to quash are requests to nullify a decision made by the same or a lower court.
A lawyer may file a motion to quash if a mistake has been made on the part of a court, or if an attorney believes that some court document such as a subpoena was not issued or delivered following the required procedure.
For example, a party that receives improper service of process may file a motion to quash.