Privacy is the prevention of allowing information to be publicly available or known more than is desired or necessary and is only meant for those whom it is intended or directly relates to.

“Privacy is necessary for an open society in the electronic age. Privacy is not secrecy. A private matter is something one doesn't want the whole world to know... Privacy is the power to selectively reveal oneself to the world.”

- Eric Hughes

From A Cypherpunk's Manifesto

http://www.activism.net/cypherpunk/manifesto.html