RSS stands for Really Simple Syndication. In a nutshell, RSS is a new way for people who publish content online to notify people interested in that content whenever fresh content is made available.
Spellhold Studios provides a RSS feed of its forums here as well as a feed of its announcements. Spellhold Studios also mirrors The Gibberling Three's Infinity Engine Modding News, which can be read here.
You will need a news reader to see the feed. Both Mozilla Firefox and Thunderbird support RSS feeds, but there are many other applications also.