A more thorough explanation:

Definition: Prior restraint is when the government stops someone from speaking or expressing themselves before they even have a chance to do so. This can happen through laws that require permits or licenses before speaking, court orders that prohibit certain speech, or outright bans on certain types of speech.

Examples:

• In Near v. Minnesota, a law allowed the government to stop a news publication from printing certain information. The Supreme Court said this law was unconstitutional, but there are some exceptions where prior restraint may be allowed, such as during wartime or if the speech would cause violence.
• In New York Times v. U.S., the government tried to stop newspapers from publishing classified documents. The Supreme Court said the government couldn't do this unless they could prove that the publication would cause immediate danger to the United States.
• In Hazelwood School District v. Kuhlmeier, school officials tried to stop a student newspaper from publishing certain information. The Supreme Court said that schools have more control over student-run newspapers than the government has over professional newspapers.

These examples show how the government can't just stop people from speaking or expressing themselves without a good reason. The Supreme Court has said that prior restraint is usually not allowed, except in certain situations where there is a real danger to the country or to people's safety.