What is public writing?

When I first hear, "public writing," I think of ANY writing that can be seen to the general public, such as books, advertisements,and newspapers. I think that public writing will be seen by people that will judge your writing and could help you establish credibility. I don't find writing regular papers public because the only people that will see them are you and your teacher. I think these blogs are a great example of public writing because anyone could find your blog (hey, it's the internet! Just hope it's not a creepy stalker-person,) and people can judge you based on what you say.