Put simply, an "RSS feed" is a format for distributing and gathering content from sources across the Web, including newspapers, magazines, and blogs. Web publishers use RSS to create and distribute news feeds that include links, headlines, and summaries. In other words, it is a format (in XML) for syndicating Web content so as to allow Web site owners and independent publishers the ability to easily share information. The idea is that when the published RSS feed changes, the content fed to your Web site will automatically change too.
Even though it may sound complicated at first, it is a rather simple technology that allows Web publishers to have other people's content aggregated and displayed on their own Web pages, without having to know XML. An RSS aggregator is a program that reads RSS documents and displays new items. It is another way to increase traffic to your Web site by offering your users content that is constantly changing (so they will keep coming back). Syndicated content includes such data as news feeds, events listings, news stories, headlines, project updates, excerpts from discussion forums and even corporate information. At the same time, it is also a way for authors and publishers to syndicate their content for others to view via a software program called an RSS Reader.
Originated by UserLand in 1997, and subsequently used by Netscape, you've most likely seen RSS feeds on one of many Web sites including: the BBC, CNET, CNN, Disney, Forbes, Motley Fool, Wired, Red Herring, Salon, Slashdot, ZDNet, and more. Think of it as a box you put on your Web page that is able to update itself: Whenever the source of the information changes, your Web page changes too, without you having to do a single thing to change it. Think of it also as a program you download (an RSS Reader) in which you subsequently sign-up for RSS feeds of interest to you; they will automatically get sent to your Reader each time they are updated.