What does "Public" mean?
If you're comfortable making something you share open to anyone, choose Public from the audience selector before you post.
Something that is Public can be seen by people who are not your friends, people off of Facebook, and people who view content through different media (new and old alike) such as print, broadcast (television, etc.) and other sites on the Internet. When you comment on other people’s Public posts, your comment is Public as well.