In the world of computers and the internet, an RSS Reader, or Feed Reader, or Feed Aggregator, or News Reader or even just Aggregator, all refer to the same concept of using a piece of software or a Web application that collects web content such as blogs, news headlines, audio broadcasts, pictures, etc., and presents them for you on your computer without you needing to visit all the sites that the content is coming from.
A loose analogy would be that it’s sort of like an email inbox. Except you control what’s coming into it. (No spam!) You can subscribe and unsubscribe from RSS feeds at your leisure and no one gets mad if you don’t answer, because there’s nothing to answer!
The major search engines provide free RSS readers, and web browsers (like Firefox and Internet Explorer), have RSS reader applications built in. There are also lots of other free software readers, too. (Do you get the notion that a lot of folks have considered that this is a cool idea?)