Official Google Blog: Surfacing forum posts in search results

Today, Google introduced a new search feature that makes it easier for you to find forum posts or discussions related to what you're searching for. This new addition to Google search results applies to sites that tend to have a large number of posts on a specific topic. When several different discussions on a site are relevant to your query, we indent them under the primary result and include the date of each post.

Official Google Blog: Surfacing forum posts in search results