Im gonna update the graphic soon to mke it flow better, but its a really neat feature.
Its basicly called "Multi-quote"
It will allow you to quote multiple separate messages at one time. If you click it, the icon will turn red, meaning that post will be quoted when you make a reply.
You can click that icon as you are reading posts and quote 2, 3, 4, whatever number of posts and when you hit the reply button the system will automaticly place all the quotes together in your post you can easily respond to multiple posts in one response.