ARG or alternate reality game is an interactive narrative that uses the real world as a platform and uses transmedia storytelling to deliver a story that may be altered by participants' ideas or actions.
The form is defined by intense player involvement with a story that takes place in real-time and evolves according to participants' responses. Subsequently, it is shaped by characters that are actively controlled by the game's designers, as opposed to being controlled by artificial intelligence as in a computer or console video game.
Players interact directly with characters in the game, solve plot-based challenges and puzzles, and collaborate as a community to analyze the story and coordinate real-life and online activities. ARGs generally use multimedia, such as telephones, email and mail but rely on the Internet as the central binding medium.
ARG is also the name of the IRC channel (chat room) on Freenode for the OTP22 discussion.
For more information on ARGs read the full article here http://en.wikipedia.org/wiki/Alternate_reality_game