This means you've started writing a blog post, but haven't saved it as a draft or published it yet, it is still active.
This sheet means that this post is currently a draft, it has not been published yet.
If you're using Evernote this is the icon you will see for all drafts synced to your Evernote account.
This appears when you still have changes that you either haven't saved to an unpublished post, or updated to an already published post.
I'm sure you've guessed it, this means the post has been published to your blog!
This means that for some reason there is a conflict with the post. The most common issue is when changes have been made to the local copy, and also to the WordPress copy.
When you schedule your posts you get this calendar as the icon. It means it will be published, but at a later date/time.
Well Blogo does more than just blog posts! This icon indicates a Page.