Basically, an ARG, or lternate eality ame, is a story-based game that integrates traditional media (books, websites, movies, etc.) into the playing experience. For example, you might have to solve a riddle in a real life location, but the answer to it may be hidden in a cryptic clue on a website.
What are your thoughts about these types of games? Have you ever played one? I have been interested in trying one of these games out, but I haven't had the time or resources (or people skills, real world or online) to participate.
Here's a link to a Wikipedia article, in case you want to learn more: