Thread:Mathmagician/@comment-4795804-20121001204055/@comment-4674838-20121001204918

The help page at Help:Wiki-style forums has a good introduction. The  tag comes from the DPLForum extension (as described on the help page and listed at Special:Version with other extensions enabled on your wiki).

Since it's a MediaWiki extension, it's a good idea to look for more information about it on mediawiki.org. In this case, mw:Extension:DPLforum should have a more complete list of parameters.