It stands for something (Really Simple Syndication?). It basically allows you to see new messages posted to a topic in an RSS reader. Most web-browsers and email programmes now have RSS readers (I use Apple Mail for example). Normally you can drag the RSS link (which should be a little orange icon - no idea why that isn't appearing) into the RSS reader. You then get a thing that tells you how many new posts there are, without having to keep going back to the website.
If you want to pick up any messages on any boards, you can use the link
www.dbmm.org.uk/forums/index.php?type=rss;action=.xml as the RSS feed link.
Have a look on wikipedia for an better explanation of RSS...
