A Writ is an emergency request for the court to review something, right now. It is taken from a pre-judgment decision by the judge.
A Writ is taken when the issue is too important to leave until the end of the case.
Writs are filed as Petitions. They request the Appellate Court to direct the Trial Court (where all Criminal cases are heard) to do something or not do something. The Writs that direct the Trial Court to do something are called Writs of Mandate. The Writs that direct the trial court not to do something are called Writs of Prohibition.
There is also a Writ of Habeus Corpus. Literally, Habeus Corpus directs the Trial Court to bring the Defendant before the court because they are being wrongly held. Habeus Corpus is used to review the constitutionality of the Trial Court’s decision.