A feed is a function of special software that allows "Feedreaders" to access a site automatically looking for new content and then posting the information about new content and updates to another site. This provides a way for users to keep up with the latest and hottest information posted on different blogging sites. Some Feeds include RSS (alternately defined as "Rich Site Summary" or "Really Simple Syndication"), Atom or RDF files. Dave Shea, author of the web design weblog Mezzoblue has written a comprehensive summary of feeds. Feeds generally are based on XML technology.

Reference http://codex.wordpress.org/Glossary