Confidentiality, the requirement that particular ‘information’/ ‘data’ be restricted to the appropriate people/systems.
The way this achieved most often is by:
Labeling information so that people understand who is allowed to see it and who should not.
Confidentiality is maintained with encryption as only those with the right key are able to decrypt it.
Destruction of the encryption key, over writing of the file multiple time, shredding paper (cross cut), crushing/mincing of hard drives are effective ways of disposal of information and maintaining confidentiality.