"A virtual world is the content of a given medium. It may exist solely in the mind of its originator or be broadcast in such a way that it can be shared with others. A virtual world can exist without being displayed in a virtual reality system (i.e., an integrated collection of hardware, software, and content assembled for producing virtual reality experiences)–much like play or film scripts exist independently of specific instances of their performance. Such scripts do in fact describe virtual worlds. Let’s carry the analogy further. We can refer to the script of a play as merely the description of a play. When that description is brought to life via actors, stage sets, and music, we are experiencing the play’s virtual world. Similarly, a computer-based virtual world is the description of objects within a simulation. When we view that world via a system that brings those objects and interactions to us in a physically immersive, interactive presentation, we are experiencing it via virtual reality."