virtual reality
     n : a hypothetical three-dimensional visual world created by a
         computer; user wears special goggles and fiber optic
         gloves etc., and can enter and move about in this world
         and interact with objects as if inside it
Source: WordNet® 2.0

virtual reality n. 1. Computer simulations that use 3-D graphics and
   devices such as the Dataglove to allow the user to interact with the
   simulation. See {cyberspace}. 2. A form of network interaction
   incorporating aspects of role-playing games, interactive theater,
   improvisational comedy, and `true confessions' magazines. In a virtual
   reality forum (such as Usenet's alt.callahans newsgroup or the {MUD}
   experiments on Internet), interaction between the participants is
   written like a shared novel complete with scenery, `foreground
   characters' that may be personae utterly unlike the people who write
   them, and common `background characters' manipulable by all parties. The
   one iron law is that you may not write irreversible changes to a
   character without the consent of the person who `owns' it. Otherwise
   anything goes. See {bamf}, {cyberspace}, {teledildonics}.


Source: The Jargon File