Google’s Webmasters blog has a post on rich snippets and structured data. While this is from Google, Microsoft’s Bing search engine has a very similar approach.
Snippets are “the few lines of text that appear under every search result” that are designed to “give users a sense for what’s on the page and why it’s relevant to their query.” The post points out that the search engine needs to understand the content on a page in order to produce the snippets.
“The snippet for a restaurant might show the average review and price range; the snippet for a recipe page might show the total preparation time, a photo, and the recipe’s review rating; and the snippet for a music album could list songs along with a link to play each song.
You can help search engines understand key information in the content by adding structured data in several formats (Google looks for Microdata (preferred), Microformats and RDFa) and for a small set of topics. These topics are those covered by schema.org: Reviews, People, Products, Businesses and organizations, Recipes, Events and Music.
See the full post for details and links.