A forum is like a message board you see in a grocery store. In fact, on many websites a forum is called ‘Message Board’ or ‘Message Boards’. People post messages and other people can reply to those messages. At its core, this is what a forum is.
Contrary to social networks, there doesn’t seem to be a real abundance of general purpose forums with a BBW section in them. At least I have never come across them. So most forums you see on the Internet are about a dedicated subject, such as BBW.
A BBW forum therefore is often very much specialized, with (sub)forums dedicated to all kinds of related subjects such as relationships, where to buy BBW clothing, dating experiences and the like.
Below are external links to some of the popular BBW forums:
More links to BBW Forums may be found on the BBW Links page by sorting the FO column (see this Blog post for more information).