Someone who's prying has a tendency to snoop into other people's private business. You may notice your prying neighbor peeking through his curtains whenever you have company.
It's human nature to be curious, but when curiosity is taken too far, it's prying. Any crime or disaster is inevitably followed by crowds of prying reporters; and you might grow used to hiding your diary from the prying eyes of your little sister. Prying and its root, pry, come from prien, "to peer in," which may trace back to the Old English bepriwan, "to wink."