I don’t think that has ever been completely explained. I did find this, but it’s about your own highly rated posts and doesn’t go into details.
Mark Katzbach
Community Special Operations
Highly rated posts is a bit of a misnomer (though don’t feel bad!). The page shows all of your posts that have been +1’d by anybody else in descending order from highest number of +1s. So, at least one person agreed with what you had to say for each of the posts on that page.
You can also make that page and the one of posts you have +1’d public through a setting in Edit Profile, if you desire.
And this: The original post can be found here.
“…there are two levels of popularity, categorized “popular” and “very popular”.Currently these are indicated by a thumbs-up icon that appears next to the +1 button. If a post is very popular, the thumbs-up earns a star that appears within said icon.
Our future plans include updating these indicators to something more visually striking. Until then, this is how you will know if a post has achieved popular status.
There are also two levels in which posts are gauged for popularity, on a per-thread basis and forum-wide. Forum-wide popularity takes into account +1s from within a set time period across the forum. Per-thread popularity takes into account all +1s in a thread. Visually, a forum-wide popular post will have a red underline beneath the thumbs-up icon".
