An RSS Feed is a content stream from a website that anyone can subscribe to. By subscribing to an RSS feed, you can stay up-to-date on any new content added to the site without having to visit the site often to see if it’s been updated.
The easiest way to read a feed is with an RSS Feed reader like Google Reader, Bloglines, NewsGator and others.
Want to know more? Try this video: RSS Feeds in Plain English.