The more popular chats aren't special scheduled topic chats. In these unmonitored chatrooms, the conversation can quickly deteriorate, which probably accounts for both the chat rooms' extreme popularity among adults, and their corresponding risk to children. Held in cyber auditoriums, they're promoted heavily by the online service. In most events members can't chat directly with the guest, but can post their questions and comments to a moderator who screens the questions, submitting some for the guest's response. Some terrific people appear as guests in cyberevents, and you might even get a chance to ask them the question you've always wanted to.
Discussion boards are bulletin boards.
Just like tacking a note on a bulletin board at your local supermarket, any member can post a message on a discussion bulletin board. Then, whenever someone else wants to comment on the posting, answer the question or add a question of their own, they can post a reply or another message to the board. Instead of using thumbtacks and scribbled index cards, online service members use electronic posts. It's more high tech, but really the same thing. Chatrooms and discussion boards are two of the biggest draws for online service providers.