RSS stands for "Really Simple Syndication". It is a way to easily distribute a list of headlines, update notices, and sometimes content to a wide number of people. RSS is a better way to be notified of new and changed content. Notifications of changes to multiple websites are handled easily, and the results are presented to you well organized and distinct from email.
RSS works by having the website author maintain a list of notifications on their website in a standard way. This list of notifications is called an "RSS Feed". People who are interested in finding out the latest headlines or changes can check this list. Special computer programs called "RSS aggregators" have been developed that automatically access the RSS feeds of websites you care about on your behalf and organize the results for you. (RSS feeds and aggregators are also sometimes called "RSS Channels" and "RSS Readers".)
RSS provides very basic information to do its notification. It is made up of a list of items presented in order from newest to oldest. Each item usually consists of a simple title describing the item along with a more complete description and a link to a web page with the actual information being described. Sometimes this description is the full information you want to read (such as the content of a weblog post) and sometimes it is just a summary.
For example, the RSS information for headlines on a local news website could contain the following information:
Title: Sidewalk contract awarded
Description: The city awarded the sidewalk contract to Smith Associates. This hotly contested deal is worth $1.2 million.
Title: Governor to visit
Description: The governor is scheduled to visit the city on July 1st. This is the first visit since the election two years ago. The mayor is planning a big reception.