Ad-hoc forums are useful if you want to enable users to add comments to some page or article, but you do not want to create the forum for each document manually. You may also consider using Message boards for this purpose if you don't need a structured forum.
Ad hoc forums can be added using the Forum (Single forum - General) web part.
If you place the Forum (Single forum - General) web part to a page and set its Forum name property to ad-hoc forum (or ad_hoc_forum if you are using ASPX templates), the forum will be displayed on the website, but it will be actually created after some visitor adds a first post to the forum. After that, the forum will be created in the AdHoc forum group forum group in CMS Desk -> Tools -> Forums.
Ad-hoc forums are uniquely identified by the document they belong to.
The following two web parts are deprecated, and they are available only because of backward compatibility with versions prior to 4.0:
•Forum (Single forum - Flat layout) - this web part ensures backward compatibility with the former Forum thread list web part
•Forum (Single forum - Tree layout) - this web part ensures backward compatibility with the former Forum tree web part