Discussion forums have been around on the internet almost as long as there’s been an internet. They offer a way for members to communicate with each other through a threaded discussion, making it easier to keep track of written conversation, as opposed to using email.
Every Group in the network contains its own forum. If someone posts something to a forum you are active in, you’ll know about it through your activity stream, or via email if you’ve chosen to track updates to that group.
Group members also have the ability to favourite any discussions they’re involved in, and see any topics they’ve started, or replies they’ve made.