The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol (APP for short) is a simple HTTP-based protocol for creating and updating Web resources.
Web feeds allow software programs to check for updates published on a web site. To provide a web feed, a site owner may use specialized software (such as a content management system) that publishes a list (or 'feed') of recent articles or content in a standardized, machine-readable format. The feed can then be downloaded by web sites that syndicate content from the feed, or by feed reader programs that allow Internet users to subscribe to feeds and view their content.
A feed may include headlines, full-text articles, exerpts, summaries, and/or links to content on a web site, along with various metadata. Feeds published in the Atom syndication format are sometimes called Atom feeds, Atom streams, or Atom channels.