Describes structured data markup that operators can add to existing HTML so that search engines can better understand the information that is contained on each web page. Major search engines use this markup to present richer search results, allowing users to more easily find the information they are looking for. In the example below, the search result shows a star rating, the number of votes, the price and the platform supported because Rich snippets were employed. (See also Meta Description).
Source: HSMAI CHDM Study Guide