Highly classified or secret information that must be kept confidential (e.g., state secrets, corporate confidential information).
その資料は機密扱いで一般には公開されていない。
That document is treated as confidential and is not publicly released.
機密情報の漏えいは会社に重大な損害を与える。
Leaks of confidential information can cause serious damage to a company.
機密文書には取り扱い方法が厳しく定められている。
There are strict rules on how to handle classified documents.