Board Chat is the place where Board Members can discuss ideas or just chat about things that are not related to any particular card.
To enter the chat, select it in the Board views.
All functionality that you would expect from a Newsfeed is there: Mentioning, Likes, Replying, Sorting by newest post or thread. You can also add Rich text to your messages. Of course, you will never miss a conversation because the Board Chat is integrated with your notifications counter.