Session group for unread messages

I would like to see a more concise filter option for unread messages. The only reason I figured out that Unacknowledged Events meant messages is because I took a wild guess. Not even the information listed in creating a Session Group explains what Unacknowledged Events means. Really, a label like that could mean literally anything. For a crazy example, "there's an info notice in Event Viewer that hasn't been read".