RSS refers to Really Simple Syndication. In more simple terms, RSS is a way of subscribing to a website. Every time the site is updated, the update is sent to you which saves you the effort of remembering to check back regularly.
You read RSS in software called a news reader, which can be either desktop or web-based applications. Popular web apps include Google Reader (my personal choice) and Bloglines. Examples of desktop apps are FeedDemon on Windows and NewsFire on the Mac. Most web browsers like Firefox, Opera, Internet Explorer and Safari include RSS readers, as do email applications like Thunderbird (cross platorm) and Apple Mail.
My RSS feed is brought to you by the Feedburner service. I choose to use Feedburner because they offer to users a variety of statistics about items in my news feed. This enables me to track what you guys are reading which in turn means that I can provide the type of content that you want to read.