Confidentiality has been defined by the International Organization for Standardization (ISO) as "ensuring that information is accessible only to those authorized to have access" and is one of the cornerstones of Information security. Confidentiality is one of the design goals for many cryptosystems, made possible in practice by the techniques of modern cryptography.
Confidentiality also refers to an ethical principle associated with several professions (eg, medicine, law, religion, journalism,…). In ethics, and (in some places) in law and alternative forms of legal dispute resolution such as mediation, some types of communication between a person and one of these professionals are "privileged" and may not be discussed or divulged to third parties. In those jurisdictions in which the law makes provision for such confidentiality, there are usually penalties for its violation.
Confidentiality of information, enforced in an adaptation of military's classic "need-to-know" principle, forms the cornerstone of information security in today's corporates.

History of the English law of confidentiality
Prince Albert v Strange (1848) 1 Mac. & G. 25 Saltman Engineering Co. Ltd. v Campbell Engineering Co. Ltd. (1948) 65 R.P.C. 203 Attorney-General v Observer Ltd [1990] 1 A.C. 109 Campbell v MGN Ltd [2004] 2 A.C. 457