Definition
RSS is an XML-based format for syndicating web content: a site organizes titles, summaries and links into a feed file, and subscribers poll that file with a feed reader to pick up updates. The RSS 2.0 specification is maintained by the RSS Advisory Board.
How it works
A site publishes an RSS file at a fixed URL and updates it as content changes; the reader requests the file at a set interval, notices new entries and presents them. The whole process is pulled by the user and does not depend on platform recommendation algorithms.
Usage
RSS is used to subscribe to blogs, news and podcasts. Podcast distribution is built on RSS: episode audio and links to show notes reach every podcast client through the feed.
Related and confusable terms
RSS and Atom are two coexisting syndication formats: Atom was standardized by the IETF in RFC 4287, the two are semantically close, and most feed readers support both.