Best described as a torrent of little children running around in a minefield (users), some armed with weapons (moderators), forums are the flagship of internet discussion, spam, and flame wars.
Smaller forums tend to be more habitable, but the larger ones have many distinct and similar features. For example, within approximately seven seconds of the creation of a topic, you will have at least one reply, garunteed. Large forums also tend to spawn makeshift caste systems within themselves, and you're automatically a malefactor in the forum until you have a 4-digit post count.
A forum can sometimes be helpful, but normally they become a time consuming and frustrating thing if you pay too much attention to them.
I got banned from that forum for being a n00b.