A significant portion of the internet space comprises of what are called as online discussion boards or forum sites. And quite a large number of people can be found active on these sites. There are endlessly long list of areas on which these sites are based on.
Starting from taking care of your pet to your own dressing and grooming; books, music, movies to electronics, academic studies to every other educational stuffs like how to do certain things, how to fix up things and finally to the really serious ones discussing businesses and ways to succeed in whatever you do, or the healthcare with proper guidance from doctors and physicians, and so on, you'll find every kind of online discussion board.
You simply have to type the field in the search bar of any search engine and you'll be shown several pages full of various different discussion boards. These are basically the places where you'll find people with similar type of interest coming together to hold on some kind of conversation, discussing certain topic , and sharing each other's ideas and viewpoints.
One can join a forum for various reasons. One can be present there for clearing up the dilemmas related to certain things, or for enhancing their knowledge base with the latest technology, or discussing the prices of a certain products, or perhaps for learning new things, it can be just anything depending upon your requirements.
But lately, people are joining up these sites for the sake of the promotional activities. Yes, you can also think of discussion forums as best possible place for your promotional and SEO activities. It works, and it doesn't just work but works quite well. But you'll have to do it in the right way for best results.
First, you need to remember that online forums are open to all, they usually don't require you to pay any fee, and it is super easy to join them up. So all kinds of people can come and join a forum and start discussions. This is why they have special moderators to keep the useless stuffs away. So you need to keep your posts written in proper way that strictly adheres to the rules and guidelines of the forum.