A threaded discussion occurs as people leave comments on a forum topic (or on other comments within that topic). A forum topic is contained within a forum, which may hold many similar or related forum topics. Forums are (optionally) nested within a container, which may hold many similar or related forums. Both containers and forums may be nested within other containers and forums, and provide structure for your message board. By carefully planning this structure, you make it easier for users to find and comment on a specific forum topic.