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 programs called feed "readers" or "aggregators": the user "subscribes" to a feed by supplying to their reader a link to the feed; 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 checked, and if so, retrieve that content and present it to the user.

The initials "RSS" are variously used to refer to the following standards:

Really Simple Syndication (RSS 2.0)
Rich Site Summary (RSS 0.91, RSS 1.0)
RDF Site Summary (RSS 0.9 and 1.0)

RSS formats are specified in XML (a generic specification for data formats). RSS delivers its information as an XML file called an "RSS feed," "webfeed," "RSS stream," or "RSS channel".

Usage
Programs known as feed readers or aggregators can check a list of feeds on behalf of a user and display any updated articles that they find. It is common to find web feeds on major websites and many smaller ones. Some websites let people choose between RSS or Atom formatted web feeds; others will provide only one of the two.

Client-side newsreaders
RSS-aware programs are available for various operating systems. Client-side readers and aggregators are typically constructed as standalone programs or extensions to existing programs such as web browsers and Email readers. Many browsers have integrated support for RSS feeds. There also are other applications that can convert an RSS feed into several usenet articles, viewable through the major newsreader software such as Mozilla Thunderbird or Forté Agent.

Web-based newsreaders
Web-based feed readers and news aggregators such as NewsGator Online require no software installation and make the user's "feeds" available on any computer with Web access. Some aggregators combine existing web feeds into new feeds, e.g., taking all football related items from several sports feeds and providing a new football feed. There are also search engines for content published via web feeds like Bloglines.