A writ of prohibition is an order from a superior court to a lower court to stop trying a case due to a lack of jurisdiction or proper authority. Because court cases are screened in advance into courts that have proper authority, this type of writ is not used very often. In fact, it is very rarely used at all.
A writ of prohibition is basically like a cease and desist letter. However, instead of being issued by the court and delivered to a non-judicial party, a writ of prohibition is given to a court. So, it is a sort of in-house monitoring tool used within the legal system. An example of a writ of prohibition being used could be if a superior court discovers that an inferior court is trying a particular case that only a federal court actually has the authority to try. This could be the result of a mistake being made by the court system, or by a recent discovery of a technicality in the law.