Google 'rich Snippets'
In 2010, Google specified three forms of structured metadata that their systems will use to find structured semantic content within webpages. Such information, when related to reviews, people profiles, business listings, and events will be used by Google to enhance the 'snippet', or short piece of quoted text that is shown when the page appears in search listings. Google specifies that that data may be given using microdata, microformats or RDFa. Microdata is specified inside itemtype and itemprop attributes added to existing HTML elements; microformat keywords are added inside class attributes as discussed above; and RDFa relies on rel, typeof and property attributes added to existing elements.
Read more about this topic: Semantic HTML