RSS or Atom

Introduction
RSS is the technology behind most blogs. Having an RSS feed (a simple XML version of your page containing fields for title, publication date, link, and description or summary) would allow me to subscribe to your news service and receive updates whenever you add a new item to the site (using a tool such as Bloglines or an email client or plugin to a web browser). This is how most people receive news updates, whether from the BBC, from the Rogue Classicist, or from the Stoa Consortium. For more information see http://en.wikipedia.org/wiki/RSS or http://www.webreference.com/authoring/languages/xml/rss/intro/

Definition
RSS (nowadays) stands for Really Simple Syndication. It is implemented by means of an XML file that can be read by an RSS reader application. RSS is typically used to provide links to updates on websites that change frequently (such as blogs). Wikipedia has a good entry on the rather tangled history of RSS. The specification is available at the Berkman Center for Internet & Society at Harvard Law School.

Atom is a competing specification which is championed by Google and is, unlike RSS, an official Internet Engineering Task Force standard, see the RFC.