RSS stands for "Really Simple Syndication" and is a way to have information from a website delivered directly to you. Instead of going to the website to see what articles have been posted recently, you can use an RSS reader - either a desktop application or a web-based application - to have the information brought to you. It saves time in visiting all the sites individually, and allows the user to quickly read what they find interesting and discard what they don't.
RSS can also be integrated into other web-based services and applications. For example, you can subscribe to an RSS feed of calendar of events and be able to keep up on the new events posted much easier than if you had to visit the site on a regular basis to look for updates.
List of web-based RSS readers