A writ of prohibition is a judicial writ issued by a higher court to a lower court or tribunal to prevent it from exceeding its jurisdiction or acting contrary to the rules of natural justice. It essentially directs the lower court to stop proceedings that are already underway. This differs from a writ of mandamus, which compels an action, or a writ of certiorari, which quashes an order already made. Option A and D describe potential targets or aims of writs but not the specific function of prohibition, while Option B is irrelevant to the nature of prohibition writs.