A much-contested legal term, social value and operational rule of government, for decades privacy has continued to elude a universally accepted definition. Every culture seems to regard it differently; even distinct social classes and generations within a society can approach the issue from varying angles.
Ask a ten-year old girl in suburban America who 'her privacy' needs protection from, and you'll get a very different (but equally valid) response than a 80-year old grandmother from a former Soviet state. What each version of 'privacy' will elucidate, however, is who is perceived to have knowledge about (and hence power over) an individuals' life. That is what privacy amounts to: individual control of knowledge about one's self.
To be clear, privacy is no 'contemporary' hang-up. This is a diversionary argument floated frequently in the tech / security fields; that privacy concerns have somehow erupted in the past decade, simply on account of social media, smart phones or Edward Snowden. Not only is that premise self-serving if one works in the bureaucracy of intelligence, it's also demonstrably false.
The Latin root of privacy is privatum, an enunciated principle of civil law as early as the Roman Republic under Cicero. Privacy was a constraint on government action inscribed into England's Magna Carta of 1215. And, perhaps most famously, the individual's right to privacy is there in the Fourth Amendment of the American Constitution.
Some of the more important books on the subject include Alan Westin, Privacy and Freedom (1967), David Flaherty, Protecting Privacy in Surveillance Societies (1989), Daniel Solove, Understanding Privacy (2008), Glenn Greenwald, No Place to Hide (2014) and Laura Donohue, Privacy and Surveillance in the Digital Age (2016).