RSS (Really Simple Syndication) is a method of delivering web content to users that do not necessarily require a web browser. If you want RSS explained in plain English, then read this article to gain a greater understanding of this technology.
Users can be updated as soon as new content is added. RSS is most commonly used on blogs and news sites. Website owners can then syndicate the RSS feeds so other sites can publish the content (sometimes just the titles of the new content is published).