It's just a post with only one nonsense tag. Try making a post with a tag, say, #inkpen3579. If you now make a post with only that tag, you can't even find the post in trending in that tag, let alone anywhere else. If upvoted for some reason, even then it'll show up in trending only for that tag, — which means it won't show up for 99% of the users of Steemit. — So content like fiction, or contests, can be discussed there without really spoiling anything for anybody. My magic tag was #pencil12345.