From Wikipedia (http://en.wikipedia.org): An Internet forum is a web application for holding discussions and posting user-generated content. Internet forums are also commonly referred to as Web forums, newsgroups, message boards, discussion boards, (electronic) discussion groups, discussion forums, bulletin boards, fora (the Latin plural) or simply forums. The terms "forum" and "board" may refer to the entire community or to a specific sub-forum dealing with a distinct topic. Messages within these sub-forums are then displayed either in chronological order or as threaded discussions. In many cases a gateway allows access to the same data via an HTTP or an NNTP interface.
Such forums perform a function similar to that of dial-up bulletin board systems that were common from the late 1970s to the 1990s. Early web-based forums date back as far as 1996. A sense of virtual community often develops around forums that have regular users. Technology, computer games and/or video games, sports, fashion, religion, and politics are popular areas for forum themes, but there are forums for a huge number of topics. Internet slang and image macros popular across the internet are abundant and widely used in internet forums.
Joomla CMS has Forum extensions, the one we recommend is Kunena Forum.
Forums are now used by many business to allow for interaction between their clients and the website and company.