What are RSS or Atom Feeds?
Wikipedia defines web feeds as:
…an XML-based document which contains content items, often summaries of stories or weblog posts with web links to longer versions. Weblogs and news websites are common sources for web feeds, but feeds are also used to deliver structured information ranging from weather data to „top ten“ lists of hit tunes…
Web feeds in the form of Atom and RSS have been around for a long time and their prevalence has been steadily growing. There are millions of websites and applications that offer information in this form. In fact, chances are the majority of websites you already visit offer their content as an RSS or Atom feed.
The reason these web feeds are useful is similar to the reason a table of contents at the beginning of books and magazines are useful. Instead of needing to visit each story individually, you can see a list of short summaries and decide what is of interest to you. More importantly, you can see a list of summaries from multiple sources (say a bunch of your favorite magazines) all in one place and decide which articles from each are of interest. Imagine being able to review a summary of all the newest articles in all your favorite magazines before you buy.
But this is just part of the story. RSS and Atom feeds are also useful for abstracting the information offered by many different websites into a format that other programs can interpret. Whereas it is difficult for any given application to extract information consistently from a wide variety of differently formatted websites, it is very easy to make use of information in RSS or Atom formats. By adopting these simple information sharing standards, content publishers and application developers make their information available to other applications and content sites in ways they may never have imagined. Developers do this because it extends the exposure of their content.