RSS is a simple XML-based system that allows users to subscribe to their favorite websites. Using RSS, webmasters can put their content into a standardized format, which can be viewed and organized through RSS-aware software or automatically conveyed as new content on another website.

For example, if you go to CNN.com they offer several RSS feeds:
​ http://www.cnn.com/services/rss/

With the RSS feed feature on your website, you can add a link such as this one:
​ http://rss.cnn.com/rss/cnn_topstories.rss to your website which will display the content of the feed directly on your website.