RSS stands for Really Simple Syndication, and is essentially just a way of quickly retrieving short blurbs of text from a news site, blog, or just about any other type of site that would contain articles or pieces of information.
Most major news web sites now provide RSS feeds, as do a lot of people's blogs even.
Essentially, you get an RSS reader for your device, and then "subscribe" to an RSS feed, which comes across the same communication channels as a web site, but is generally much smaller. The RSS reader will poll for new information either on-demand or on a scheduled basis. This information will generally take the form of news headlines and sometimes even short extracts of the text from the article. Most readers will also include a link allowing you to open a web page to read the full article.
To access RSS feeds from your Blackberry, you would need an RSS reader application. I use NewsClip
for this myself, but there are several other applications that will do this as well. If you check out the Aftermarket Software
forum here on BBforums and do a quick search for "RSS" you can find several possible applications.