tags

Forums have their own vocabulary associated with them, which is created based on the forums hierarchy.
The question is whether new posts to the Forums can be tagged using terms in other vocabularies, rather that Forums' native one.

Meta tags module , a.k.a. "nodewords", allows setting some meta tags for each node, view or panels page. Meta tags is the preferred name.

Giving more attention to the important keywords and/or description on some of the nodes allows getting better search engine positioning (given that you really only provide the keywords which exist in the node body itself, and do not try to lie).

http://drupal.org/project/nodewords
http://drupal.org/node/161083