When you send out a comment on pownce, you can send to friends or make the comment public. The public post show up on other peoples profiles, even if they are not logged in. So basicaly public post are what the website shows to everyone, not just logged in users on pownce. If the post isnt' public no one else sees it but you.

I see how I was confusing, friends and fans are the public, so when you send a message to the public it is to any one related to your account.