I've been finding some confusion among people over Chat versus Forum.
It seems that some people use Chat room interchangeably with Forum and Bulletin Board. I guess it's due to discussions being done on a forum, which some might see as chatting.
In computer/Internet terms, chat is instant. Like Instant Messaging. It's transient. Like speaking on the phone, the words are gone once they leave your mouth. With a Chat Room, the text may stay visible for a minute, an hour, or a couple days, depending on how busy it is. But it is not lasting.
The Forum is preferable, as it is permanent (until you decide to manually purge messages). On a website, permanent is good because it allows people to research, to pickup old discussions, and perhaps constantly add to an old discussion. The more information, the longer someone will stay. The more information, the better your rankings in the Search Engines. And, isn't your site about information and content?
Chat Rooms are good for having a live presentation or meeting. Maybe an Ask The Chef event, where people can ask a celebrity Chef questions, live. It would be an instant interchange, a live discussion. You could then save the full dialog and post it as the 'Transcript' of the event. Other than having an event, Chat Rooms aren't productive for a website.
If you notice, with WebSpace and YouTube, and other Web 2.0 (interactive websites), a lot of sites use Commenting. Commenting allows people to leave comments on an article or topic. It's not as interactive as a forum. It doesn't allow a visitor to START a topic, but for some sites, that's preferable.
To break it down to a simple Bullet List:
Chat (Chat Room) - use only for Live events. This is slowly being replaced by Video, with webcams allowing for visual group meetings. See http://www.paltalk.com/en/ for more about Video Chatting.
Forums (Bulletin Boards) - Great place for continuing discussions. Users can usually start their own topics, ask questions, answer each other. Good forums create a sense of community, and become self-running, self-moderating. Registration is usually required for posting, simply to help prevent the forum from getting filled up my spam. If you are looking for a truly interactive website, think about adding a forum to your website.
Commenting - usually allows visitors to comment on a story/article posted by the website. This is not as interactive, since the visitor doesn't start the topic. But it is a popular way to get feedback on articles, and allow readers to voice their opinions. Many news and Blogging sites have this feature.
Blogging - an overused term that originated from 'Web Log', starting as a simplified online diary. It is really nothing more than an Article/Content generator. Usually a simple interface for the author to type their content in, and then post for the world to see. The difference between Blogging and Forums is that the blog is in the form of a Web Page/News Article display, while forums are usually in a structured format of Category/Topic/Discussion Thread. Most Blogs can look like an online magazine, with leading paragraphs forwarding you to the full article. See the 'Site News & Blog' on this site.
Blogs are really just helpful tools to make it easier to add content to your site. You can then add commenting to it.
When planning your website, and discussing features, try to review the terms above to get a better understanding of the difference. Especially when asking someone to build a site for you. You don't want to say "Chat" when you really mean "Forum".