This essay, written in 1998 by an active participant in both virtual reality development and the virtual reality definition debate, discusses the definition of the phrase "Virtual Reality" (VR). I start with history from a personal perspective, concentrating on the debate between the "Virtual Reality" and "Virtual Environment" labels in the late 1980's and early 1990's. Definitions of VR based on specific technologies are shown to be unsatisfactory. I propose the following definition of VR, based on the striking effects of a good VR system: "Virtual Reality is the use of computer technology to create the effect of an interactive three-dimensional world in which the objects have a sense of spatial presence." The justification for this definition is discussed in detail, and is favorably compared with the dictionary definitions of "virtual" and "reality". The implications of this definition for virtual reality technology are briefly examined.