What is RSS?
RSS Really Simple Syndication is a type of Web-Syndication / Feed from a website with the latest updates of its frequently changing content. Latest news, software updates, and blogs are examples of such content.
Feeds can be subscribed to with most of the latest browsers, also with online services such as My Yahoo, Google Reader, and BlogLines, bringing updates straight to your personal computer.
You can find an article in Wikipedia on RSS with general information on its usage, history and technical specification.