RSS is a format for delivering regularly changing web content.
Many news-related sites, weblogs and other online publishers syndicate their content as an RSS Feed to whoever wants it.
It allows you to easily stay informed by retrieving the latest content from the sites you are interested in. You ensure your privacy, by not needing to join each site's email newsletter.

A variety of RSS Readers are available.
Some popular feed readers include Amphetadesk (Windows, Linux, Mac), FeedReader (Windows), and NewsGator (Windows - integrates with Outlook).
There are also a number of web-based feed readers available. My Yahoo, Bloglines, and Google Reader are popular web-based feed readers.