Recent Posts should basically list everything, in time order from the most recent change, with special markings for "New" posts and "New Comments."

You will also see "updated" when the original poster updates their blog post or the head post on a forum thread, or when we update one of the web site's main pages (like the home page when an issue is released).

As Jeff said, it's everything, listed in reverse chronological order, with the most recent changes listed first.

The "updated" or "new" text marker in the recent posts listing is clickable, and you can click on that marker text to jump directly to the new content.

If i have not had time for some reason to look at a recent post, when I come back to the forum, they will still be marked as recent posts.  Sometimes if there is enough activity, the posts I missed will have moved on to page 2, but I can still access the most recent posts without having to wade through previous posts that I have already read.