Public – The post will be visible to everyone.
Stick this post to the front page – The post will be “stuck” to the top of the blog’s front page. More info about Sticky Posts below.
Protected – The post is protected with a password you set. Any user that has the password can view a protected post.
Private – Posts are only visible to blog Editors and Administrators. Private posts are not visible in Blog Surfer, feeds, or in any search. A post can be private without being password protected.
read more here . http://en.support.wordpress.com/posts/post-visibility/