RSS is a family of XML dialects for Web syndication used by (among other things) news websites and weblogs.

The technology of RSS allows Internet users to subscribe to websites that have provided RSS feeds; these are typically sites that change or add content regularly. To use this technology, site owners create or obtain specialized software (such as a content management system) which, in the machine-readable XML format, presents new articles in a list, giving a line or two of each article and a link to the full article or post. Unlike subscriptions to many printed newspapers and magazines, most RSS subscriptions are free.

The RSS formats provide web content or summaries of web content together with links to the full versions of the content, and other meta-data. This information is delivered as an XML file called an RSS feed, webfeed, RSS stream, or RSS channel. In addition to facilitating syndication, RSS allows a website's frequent readers to track updates on the site using an aggregator.

In its simplest form RSS can be described as a list of a web site's new or updated content.

RSS was originally developed to allow news services to syndicate their content by displaying headlines, links and article summaries on other web sites and through dedicated software called news aggregators.

Source: Wikipedia