## 3 The Ambiguity of Virtual Reality Terminology in Healthcare and Beyond
### Modern Definitions and Concepts of Virtual Reality and Related Technologies  
The inconsistency in terminology surrounding VR and related technologies has led authors to propose modern definitions and concepts intended to align with current technological advancements and the use of VR systems. However, even up-to-date definitions lack uniformity, despite being published within a span of just one to two years [40; 42; 43]. This lack of consensus can even be seen in the definition of the appropriate umbrella term for VR and related technologies (the most frequently mentioned besides VR are AR and MR). In the literature, the abbreviation \"XR\" is widely accepted as an umbrella term, but its interpretation varies. Some attribute XR to \"extended reality\" [60], others to \"cross reality\" [61], and some to \"X-reality\" [62], which is occasionally described as a variaton of \"extended reality\" [63; 64]. Although it is widely agreed that XR encompasses VR, AR,and MR [65; 66; 67], the relationships between these technologies are often not clearly defined, except for MR, which is typically described as a blend of VR and AR [43]. Recently, [PERSON] et al., (2022) [40] raised concerns about the term \"extended reality\", emphasizing that it fails to include VR, where the real environment is replaced rather than extended. As an alternative, the authors proposed \"X-reality\" as an umbrella term, with \"X\" functioning as a placeholder for any form of new reality. Within their framework, an AR continuum was introduced, extending from assisted reality, where virtual content appears clearly artificial, to MR, where the integration of virtual and real objects becomes seamless and indistinguishable. The concept also incorporates diminished reality, which ranges from the application of unrealistic overlays to the undetectable removal of real objects [40]. Additionally, they further outlined a VR continuum that spans from atomistic VR, prioritizing specific goals over user experience, to holistic VR, characterized by an immersive experience nearly indistinguishable from real-world interactions [40]. In contrast, [PERSON] and [PERSON], (1994) [68] proposed the reality-virtuality continuum, anchored at one end by a purely real environment and at the other by a purely virtual environment. In their model, MR is defined as the umbrella term for environments that combine real and virtual elements, excluding fully virtual environments, which are positioned at the far right of the continuum. Critics, however, argue that the virtual environment endpoint, defined by [PERSON] and [PERSON], (1994) [68] as _\"consisting solely of virtual objects\"_ and _\"completely synthetic\"_, can be fully virtual only for extroceptive senses, but not for interoceptive ones [42]. Consequently, they propose that all VR experiences should be categorized under the umbrella term \"mixed reality\", as they inherently blend virtual elements with real-world sensations (e.g., computer-generated stimuli combined with physical sensations such as gravity) [42]. Recently proposed frameworks and the present understanding of VR and related technologies are illustrated in Figure 2.  
In the field of healthcare, the term \"XR\" is widely used, with some researchers expanding its scope to include video games and related applications, in addition to VR, MR, and AR [60]. This further underscores the tendency of some researchers in this field to classify VR alongside 3D games displayed on a flat 2D screen. Accordingly, in their literature review, [PERSON] et al., (2023) [43] examined how the term VR is defined in the medical literature and proposed the following definition of VR: _\"VR is a three-dimensional computer-generated simulated environment, which attempts to replicate real-world or imaginary environments and interactions, thereby supporting work, education, recreation, and health\"_. Their definition was constructed to accommodate the current confusion in the field and to encompass the broad range of interpretations of what constitutes VR.