Confidentiality, with respect to information security, is the assurance that it will not be disclosed to unauthorized individuals. The U.S. legal definition is "Preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information." 
The restrictions, however, can become quite complex. For example, the usual commercial or civil government case is protection of disclosure of contents. In a military context, however, the very existence of the information, and of its transmission, must remain secret against the threats of traffic analysis and direction finding.
- 44 USC 3542