Full Title or Meme
Privacy is the right to be let alone. 
Everyone wants some privacy, but no one can explain that in a way that matches anyone else's desire for privacy. Privacy is associated with liberty, but also with privilege (private roads, private schools), with confidentiality (private conversations) with nonconformity, with dissent, with shame, with embarrassment, with the deviant, with the taboo, with subterfuge and concealment.
In his dissent to a 1952 Supreme Court decision Justice Douglas issued this stirring defense of the right to be let alone:
"If liberty is to flourish, government should never be allowed to force people to listen to any radio program. The right of privacy should include the right to pick and choose from competing entertainments, competing propaganda, competing political philosophies. If people are let alone in those choices, the right of privacy will pay dividends in character and integrity. The strength of our system is in the dignity, the resourcefulness, and the independence of our people. Our confidence is in their ability as individuals to make the wisest choice. That system cannot flourish if regimentation takes hold. The right of privacy, today violated, is a powerful deterrent to any one who would control men's minds."
The above statement seems to state that the people's character and integrity will be enhanced by the right to pick their own sources of information. There is ample reason to doubt that statement in light of the environment in 2018 where populist demagogues are again persuading people to vote against their own interests by manipulating news sources that appeal to the peoples' prurient interests.  But the statement does seem to clarify that privacy is about liberty, the right to do what you want with yourself and your belongings.
Technology, and social media in particular, record nearly every transaction that we make, and can retrieve it for any purpose not explicitly disallowed by regulation. The amount of information that Facebook has accumulated about people is far more that most people understand. The constantly evolving problem is to keep the laws protecting citizens from depredations by large organization up-to-date in the face of rapidly accelerating change.
The number of governments that have proposed "Solutions" to the invasions of "The Right to Privacy" is large, but the results are meager and most law enforcement agencies are often in court trying to use any loop-hole to strip away privacy even where products have been specifically designed to maintain privacy. The same laws that protect privacy also protect criminal behavior. Not that privacy laws always make sense; federal law prohibits the National Tracing Center from using a searchable data base to identify the owners of guns seized at crime scenes. No privacy advocate has recommended that law be repealed.
- Warren and Brandeis The Right to Privacy Harvard Law Review http://groups.csail.mit.edu/mac/classes/6.805/articles/privacy/Privacy_brand_warr2.html
- Louis Menand Nowhere to Hide: Why Do We Care So Much About Privacy? The New Yorker June 18, 2018 https://www.newyorker.com/magazine/2018/06/18/why-do-we-care-so-much-about-privacy
- Public Utilities Comm'n v. Pollak, 343 U.S. 451 (1952) https://supreme.justia.com/cases/federal/us/343/451/case.html
- Eduardo Porter, Is the Populist Revolt Over? Not if Robots Have Their Way https://www.nytimes.com/2018/01/30/business/economy/populist-politics-globalization.html
- Sarah Igo, The Known Citizen: A History of Privacy in Modern America 2018 ISBN 978-0674737501
- Brian X. Chen https://www.nytimes.com/2018/04/11/technology/personaltech/i-downloaded-the-information-that-facebook-has-on-me-yikes.html
- Jack Nicas Apple to Close iPhone Security Hole That Law Enforcement Uses to Crack Devices https://www.nytimes.com/2018/06/13/technology/apple-iphone-police.html