RSS is an XML-based format that allows the syndication of lists of hyperlinks, along with other information, or metadata, that helps viewers decide whether they want to follow the link.
RSS allows peoples' computers to fetch and understand the information, so that all of the lists they're interested in can be tracked and personalized for them. It is a format that's intended for use by computers on behalf of people, rather than being directly presented to them (like HTML).
To enable this, a Web site will make an RSS feed, or channel, available, just like any other file or resource on the server. Once a feed is available, computers can regularly fetch the file to get the most recent items on the list. Most often, people will do this with an aggregator, a program that manages a number of lists and presents them in a single interface.
RSS can also be used for other kinds of list-oriented information, such as syndicating the content itself (often weblogs) along with the links.