An Atom feed is very similar to an RSS feed in that it is a lightweight XML format allowing for easy syndication of web content. In fact, most RSS readers and news aggregators will be able to read Atom feeds just fine, as it is becoming a widely-used alternative to RSS feeds.
What’s a “feed”?
For those who are unfamiliar with syndication feeds (such as an Atom feed, an RSS feed or an RDF feed), they are small text files that provide information about content on websites. When content is updated, the feed text file is also updated, either manually or programatically. Applications called “readers” or “aggregators” can then check these small text files and notify someone when new content is available.
If you already have an RSS feed, creating an Atom feed is extremely easy. The primary difference between the two formats (from a developer’s standpoint) is the XML tags that are used. You can refer to Atomenabled.org for more information about the Atom specification and for information about required tags as well as available tags.