A gag order (or suppression order) is an order, sometimes a legal order by a court or government, other times a private order by an employer or other institution, restricting information or comment from being made public.
Gag orders are often used against participants involved in a lawsuit or criminal trial. They are also a tool to prevent media from publishing unwanted information on a particular topic. A National Security Letter, which is an administrative subpoena used by the FBI, has an attached gag order, restricting the recipient from ever saying anything about that they were served with one.
A Criminal Court, for instance, will issue a gag order on the media if the judge believes that potential jurors in a future trial will be influenced by the media reporting or speculation on the early stages of a case. Another example might be to ensure police are not impeded in their investigations by media publicity about a case.
A gag law is intended to limit freedom of the press, as by instituting censorship or restricting access to information. In the United States, a court can only order parties to a case not to comment on it; a court has no authority to stop unrelated reporters from reporting on a case. Most statutes which restrict what may be reported have generally been found unconstitutional and void. However, the gag provisions of the WIPO Copyright and Performances and Phonograms Treaties Implementation Act have been upheld.