RSS = really simple syndication.
Basically, it is a way to let people know about news and updates to a certain website, or website sub-section. In the not too distant past, you'd need third party software called 'feed readers' in order to view and update the RSS feeds you have subscribed to.
Now, all the new browser versions (Firefox 2, IE 7, etc.) all have built in RSS support. An RSS feed is usually just a simple .xml file.
With new browsers, you click on the RSS feed, and it'll ask you if you want to subscribe, you say yes, and it's added to your list of subscribed feeds.
Then whenever there is news, the feed is updated and you are informed instantly about it when you check your feeds.
Pretty much replacing e-mail as a way of informing a subscriber base about updates and news - without them having to actually visit a website and browse through it, looking for updates.
Because, as we have been conditioned to think, every nanosecond counts. Right? There...one just went by...how did YOU use it?
