RSS (Really Simple Syndication) is a mechanism for sharing and distributing Web content, for example news headlines. With an RSS reader you can access information, sometimes known as feeds or streams, from many different sources.
RSS readers, sometimes called aggregators, are software applications that download and display the content of RSS feeds. RSS readers can be stand alone applications or part of an existing programme (for example Internet Explorer 7.0).
Visit the RSS page on Wikipedia for more information.