I just happened upon the essay entitled "Privacy" in the Stanford Encyclopedia of Philosophy. I have always said that the definition of privacy is elusive, as it means many different things to different people, primarily based upon their background. For physicians, privacy equals confidentiality in which there is a trusted group within which information can be freely shared and used. For IT-types, privacy equals security: making sure that the bad guys don't get access to personal information. Privacy is all that and then some. In the context of more recent privacy laws (particularly Canadian ones), privacy is about confidentiality, security and -- as importantly -- giving people control over their personal information.
For a more philosophical and historical view, take a look at the Stanford essay:
"The term "privacy" is used frequently in ordinary language as well as in philosophical, political and legal discussions, yet there is no single definition or analysis or meaning of the term. The concept of privacy has broad historical roots in sociological and anthropological discussions about how extensively it is valued and preserved in various cultures. Moreover, the concept has historical origins in well known philosophical discussions, most notably Aristotle's distinction between the public sphere of political activity and the private sphere associated with family and domestic life. Yet historical use of the term is not uniform, and there remains confusion over the meaning, value and scope of the concept of privacy...."