When you create a new thread, you can now input a series of "tags". Tags are simply keywords that describe the thread.
If you then click on the tags link in the menu bar above you will be presented with what is called a "tag cloud";. The more times a tag is used, the larger the text grows. As you can see, the tags are also searchable.
Clicking on one of the tags in the cloud then lists all of the threads that are tagged with that particular keyword. The default option lists tags in a forum display format.
Clicking on the thread title of one of the above threads then takes you to the thread. The tags the thread are tagged with are also listed below the thread. Clicking one of those tags takes you to all the threads on the forum tagged with the same tag.
The forum's tags are also searchable via the search dropdown. The advanced search option allows for a variety of additional criteria to be seached for. You create a whole new (and highly efficient) forum search engine!