A being's authority over who may see what is theirs. Privacy is not secrecy — it is who decides.
Latin privatus (set apart, belonging to oneself, not held in public), from privare (to bereave, to release from), from privus (single, individual, one's own); privacy names the standing of the one who decides, not the act of hiding.
A being's own authority over who may see what belongs to them. The root does not mean hidden — it means singular, one's own — which is why privacy here is about who decides rather than about concealment.