What even is privacy, what does a right to privacy mean, and rest on?

Possibly the discussion is using the wrong vocabulary. “Privacy” is an odd name for the good that is being threatened by commercial exploitation and state surveillance. Privacy implies “It’s nobody’s business,” and that is not really what Roe v. Wade is about, or what the E.U. regulations are about, or even what Katz and Carpenter are about. The real issue is the one that Pollak and Martin, in their suit against the District of Columbia in the Muzak case, said it was: liberty. This means the freedom to choose what to do with your body, or who can see your personal information, or who can monitor your movements and record your calls—who gets to surveil your life and on what grounds.

https://www.newyorker.com/magazine/2018/06/18/why-do-we-care-so-much-about-privacy