The Free On-line Dictionary of Computing (30 December 2018):

Rich Site Summary
Really Simple Syndication
RSS
RSS feed

    (RSS, blog, feed) A family of
   standard web document types containing regularly
   updated, short articles or news items.

   RSS documents (generally called "RSS feeds", "news feeds" or just
   "feeds") can be read with an RSS reader like BottomFeeder or
   Feedly.  These are sometimes called "aggregators" because they
   combine multiple RSS feeds which the user can browse as a single
   list.  The RSS reader tracks which articles the use has read, and
   is typically set to show only new articles, hence the idea of a
   "feed" or flow of new items.

   Most RSS feeds are based on RDF.  RDF is a structured document
   format for describing textual resources such as news articles
   available on the web.  RSS originally stood for "RDF Site Summary"
   as it was designed to provide short descriptions of (changes to) a
   website.

   Because it provides a standard way to deliver, or "syndicate",
   news or updates from one site to another, RSS is sometimes
   expanded as "Really Simple Syndication".  It is closely associated
   with blogs, most of which provide an RSS feed of articles.

   (2013-08-15)