A more thorough explanation:

A government secret, also known as a state secret, is information possessed by the government that, if revealed, would be a threat to national defense or diplomatic interests of the United States. This information is of a military or diplomatic nature and its disclosure would be contrary to the public interest.

State secrets are privileged from disclosure by a witness in an ordinary judicial proceeding. This means that if someone is asked to testify in court, they cannot reveal any information that is considered a state secret.

For example, if a government official has information about a military operation that is currently being planned, they cannot reveal that information to the public or to anyone who is not authorized to know about it. This is because the disclosure of such information could compromise the success of the operation and put the lives of soldiers at risk.

Another example of a government secret is information about diplomatic negotiations between the United States and other countries. If this information were to be revealed, it could damage the relationship between the two countries and make it more difficult to reach agreements in the future.