Rich Site Summary or Really Simple Syndication (RSS) is an XML-based format used to publish and syndicate continuously changing headlines and content abstracts to the Internet. An RSS reader collects and monitors published RSS feeds to retrieve information from predefined Web sites, and maintain the information in a single location.
The use of RSS is a growing trend—it is a safe and easy way to publish and retrieve real-time information over the Internet.
Google's list of RSS Tools.