The basis for the virtual reality (VR) idea is that a computer can synthesize a 3-D graphical environment from numerical data. Using visual and auditory output devices, the human operator can experience the environment as if it was a part of the world. This computer-generated world may be either a model of a real-world object, such as a house, or an abstract world that does not exist in a real sense but is understood by humans, such as a chemical molecule or a representation of a set of data, or it might be in a completely imaginary science fiction world. Further, because input devices sense the operator's reactions and motions, the operator can modify the synthetic environment, creating the illusion of interacting with and thus being immersed within the environment.

These characteristics also allow a definition of VR in terms of human experience: a real or simulated environment in which a perceiver has the experience of presence in an environment by means of a communication medium. This definition clarifies the possible role of VR in medicine: a communication interface based on interactive 3-D visualization, able to collect and integrate different inputs and datasets in a single real-like experience.