Rich Snippets are small previews of relevant information on your website that display in the search results when someone performs a search.
Rich snippets tell the search engines more about your website and what content you have on your pages. It will display a main headline link at the top of the search listing and a few lines of what’s on the page directly below the link. To show Rich Snippets, Google looks for markup formats (microformats and RDFa) that sites can add to pages to make this structured data available on the search results.
Websites can use these rich snippets to provide additional information in search engine results for consumers who were looking for something, and affect the ROI of the websites.