RSS

What is XML?
Wikipedia defines it as
The Extensible Markup Language (XML) is a general-purpose markup language.[1] Its primary purpose is to facilitate the sharing of data across different information systems, particularly via the Internet.[2]
It is a simplified subset of the Standard Generalized Markup Language (SGML), and is designed to be relatively human-legible. By adding semantic constraints, application languages can be implemented in XML.
What is RSS?
RSS is a family of web feed formats used to publish frequently updated digital content, such as blogs, news feeds or podcasts.
Users of RSS content use software programs called "feed readers" or "feed aggregators". The user subscribes to a feed by entering a link of the feed into the reader program. The reader can then check the user's subscribed feeds to see if any of those feeds have new content since the last time it was checked, and, if so, retrieve that content and present it to the user.