Rich Site Summary, Really Simple Syndication, RSS 1.0, RSS 2.0, PodCasting are all ways to say have an XML document that lists an index of recent web site additions that can be systematically captured by external sites or services.
RSS is no longer a new technology which has succeeded far beyond where PointCast had could of planned. However, the power RSS has is to begin to seep back into the documents it seeks to index. In other words, well formed web pages can make RSS less necessary. See RESTful architecture to understand the real power of RSS.
On the other hand RSS is often not human readable (except with browsers that mess with them), but could be with XSL. Making them human readable would have helped with making them more popular with non-geeks as well as easier to explain.