A writ of certiorari is a form of judicial review whereby a court is asked to consider a legal decision of an administrative tribunal, judicial office or organization (eg. government) and to decide if the decision has been regular and complete, if there has been an error of law, if the tribunal had the power to make the decision complained of or whether the tribunal exceeded its powers in issuing the decision complained of.
For example, a certiorari may be used to wipe out a decision of an administrative tribunal which was made in violation of the rules of natural justice, such as a failure to give the person affected by the decision an opportunity to be heard.
Certiorari, if the application is succesful, renders the decision at issue of no force or effect and null and void. Lawyers say it is quashed.
The companion remedy is prohibition, which asks that an anticipated or prospective decision, alleged to be ultra vires, be stopped before it issues.
Certiorai is one of the five traditional remedies available in administrative law.