# Metaverse Architectures: A Comprehensive Systematic Review of Definitions and Frameworks
## 1 Introduction
### Contributions  
The topic of the metaverse has attracted considerable research attention. To date, several papers have emerged from various aspects of the metaverse. For example, [PERSON] and [PERSON] [21] conducted a comprehensive review of existing literature, suggesting definitions that emphasised 3D environments and the convergence of technologies. [PERSON] [36] identified decentralisation, immersion, and shared environments as key components. [PERSON] et al. [35] developed a framework that highlighted the evolving social and technological aspects of the metaverse. [PERSON] et al. [51] employed a methodology to identify key themes in a large text corpus, highlighting important metaverse characteristics such as collaboration, synchronisation, and the integration of real and virtual elements. Similarly, [PERSON] et al. [52] and [PERSON] et al. [53] conducted reviews that revealed differences in academic definitions while also identifying common concepts such as user engagement, content creation, and effects on cognitive processes. [PERSON] [54] defined the metaverse by emphasising interconnected virtual worlds, immersion, scalability, and economic infrastructure. On the other hand, some academic studies have mostly focused on key requirements, describing the architectural infrastructure of the metaverse and closely examining its technical and design aspects. [PERSON] and [PERSON] [41] present a comprehensive overview of the Metaverse, including its requirements, architecture, and standards, as well as its challenges, open problems, and perspectives. [PERSON] and [PERSON] [55] discuss the taxonomy of technologies in the metaverse, classifying the Metaverse components and major approaches into hardware, software, content, user interaction, implementations, and applications. Some articles [5; 56; 57] explored focus on enabling technologies and general architecture in the metaverse. Moreover, [PERSON] and [PERSON] [58] report on the latest applications of the metaverse technology, concerns and technical challenges. Those papers primarily focused on an overview of the metaverse, its requirements, technologies, and proposed architecture; however, they lacked a unified architecture and a domain-agnostic framework that systematically integrates interoperability, governance, privacy, and technological scalability. This research critically examines the definition and architectural conceptualisation of the Metaverse within academic literature. Addressing the persistent lack of consensus regarding both its definition and architecture, this study employs a systematic literature review to synthesise existing scholarly perspectives. The primary contributions of this study are as follows:  
* First, a systematic review of the literature is undertaken to investigate the definitions and architectural frameworks of the metaverse within academic research. This enables the synthesis of current definitions and the identification of various proposed architectural models, thereby establishing a fundamental comprehension of conceptual and structural patterns. * Second, a word frequency and thematic analysis is conducted on 33 metaverse definitions, culminating in a refined, generalised definition. Based on prevailing viewpoints, these definitions are then categorised into five specific types: technological orientation, spatial-environmental design, social and human interaction, economic and ownership systems and conceptual and linguistic constructs. * Third, 25 architectural models are analysed and subsequently categorised into layered-based, technology-based, and domain-based classifications. A comparative evaluation is then conducted on the prominent three-layer, four-layer, and five-layer general-purpose architectures to ascertain structural depth and thematic coverage. * Finally, we critically assess the gaps and limitations in existing architectures, particularly the absence of dedicated governance mechanisms and limited support for interoperability in earlier models.