Atom is an XML-based web syndication format, similar to RSS, for providing the updated contents of web pages to Internet users. This means that users can automatically receive all updates to the contents of a web page the instant the update comes online.
Most popular web browsers (e.g., Internet Explorer, Mozilla Firefox) offer the ability to subscribe to Atom feeds, and will prompt you when one is encountered. Feed readers, programs that support subscribing to feeds outside of a web browser, are another option.