RSS is a family of Web feed formats used to publish frequently updated works—such as blog entries, news headlines, audio, and video—in a standardized format. An RSS Feed includes full or summarized text or audio attachments (podcasts) and video attachments (video podcasts). By subscribing to an RSS feed readers get timely updates from their favorite websites and can aggregate feeds from many sites into one place. RSS feeds can be read using software called an "RSS reader", "feed reader", or "aggregator", which can be web-based, desktop-based, mobile device or any computerized Internet-connected device.
Wikipedia has a helpful entry on RSS that tells you what RSS is all about. Google/YouTube has some good videos that explain RSS and RSS Readers. For a quick, light-hearted overview, watch RSS in Plain English. For a rich, detailed how-to guide, watch What is RSS? from the Peoria, AZ school district.
How do I pick an RSS Reader?
There are many choices available but the first decision is whether to select a web-based or desktop-based reader. Each offers different benefits.