RSS is a special kind of markup that enables sites to produce summaries of their content that can be “fed” to other sites or to applications designed to read them. This can be quite useful because it provides a way to check an RSS-enabled site’s content without having to visit that site. When subscribing to a large number of RSS “feeds” from a large number of sites, this makes it possible to see which ones have new or interesting content without having to visit each individual site—which can be a real time-saver!

For more information about RSS, please see the this description at Software Garden.