ABSTRACT
Defining virtual reality is an indispensable task. In literature, we still find definitions that inappropriately mix the purpose of virtual reality, its functions, applications and the techniques on which it is based. We must reject these approaches, firstly because they are centred on only one particular technology, and secondly because they are extremely restrictive in terms of scientific issues related to the complexity of the dimensions involved in the interaction between the human user and the virtual environments. We have given definitions with various levels to give a clear picture of the domain of virtual reality.
