According to the Encyclopedia Britannica Online, an RSS feed stands for either really simple syndication or rich site summary. "RSS is a format used to provide subscribers with new content from frequently updated Web sites."
So let's say you really like to know what's going on in the education columns of the New York Time's online but don't like to spend time checking the website every day. By subscribing to the column's RSS feed, any new content will automatically be sent to your RSS feed reader, such as Bloglines or Google Reader.
You can then read all of your feeds in one place by visiting your reader. This means you don't have to spend the time checking each website that is of interest to you. It's like a publication alert that is sent directly to you.
"RSS." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 23 Mar. 2009 <http://search.eb.com/eb/article-9471623>.
This video from Common Craft explains RSS feeds.
Many websites and databases now have RSS feeds. Look for this logo:
or anything similar to these below:
Source of above image: http://www.rssboard.org/rss-icon-collection
You might also look for an "alerts" button. Database vendors often use this term.