Also known as boards, discussion boards, message boards, or discussion forums, forums are collections of community-driven discussions. Forum software solutions vary greatly, but often a forum offers topics with threaded conversations, and require contributors to register an account in order to take place in discussions. Forums are similar to email mailing list discussions, and bulletin boards.
Often targeted towards one topic or niche, forums are usually meant to be places of polite discourse between like-minded people. Often one or multiple community members are appointed moderators, and they police the forum, to make sure users and discussions follow forum rules.
In addition to being a great way to form a community around a website, a forum can provide great content for a search engine to index, sending additional traffic to a website.