# Metaverse Architectures: A Comprehensive Systematic Review of Definitions and Frameworks
## 1 Introduction  
With the expansion of studies on three-dimensional (3D) mixed reality (MR), virtual reality (VR), and augmented reality (AR), the metaverse has garnered significant interest from various institutions and organisations worldwide, aiming to develop immersive environments and facilitate real-time communication through these technologies. The term \"metaverse\" was historically used by [PERSON] in the 1992 science-fiction novel Snow Crash, where people use virtual reality to access a shared digital world [1]. In its history, the metaverse has evolved from a theoretical concept to a pivotal element in the technology and entertainment industries. This evolution came from advances inonline multiplayer gaming, VR, AR, and artificial intelligence [2]. Linden Lab [3] introduced the first virtual world with Second Life in 2003, and Roblox [4] launched in 2006 an online multi-user platform that allows users to create and play games developed by others. Another notable literary work that gained significant attention was [PERSON]'s Ready Player One, published in 2011 and later adapted into a film [5]. The film portrayed a future in which individuals utilised haptic gloves and a VR headset to escape their mundane lives and enter a virtual world where they can experience tactile sensations [6]. Microsoft, Nvidia, and Meta subsequently introduced prototypes for the metaverse in 2021 [7]. Microsoft launched Mesh for Teams to enable immersive, mixed-reality communication in workplaces [8]. Similarly, NVIDIA introduced the Omniverse platform, designed to integrate 3D environments into a collective virtual reality [9]. Meanwhile, following its rebranding from Facebook, Meta launched Horizon Worlds, a virtual reality social platform designed to promote user engagement and collaborative content creation [10]. Currently, there is no consensus on the exact definition of the metaverse topology [11; 12; 13; 14; 15], as various interpretations exist, and hence, no standard definition has been established [16; 17]. The absence of a unified definition of the metaverse stems from multiple interconnected factors, reflecting its dynamic nature and the diverse perspectives of stakeholders such as academics, technologists, and industry leaders [18; 19]. Diverse individuals, institutions, and organisations define the metaverse according to their specific contexts and objectives, resulting in a multitude of definitions that reflect varying perspectives [20]. Consequently, scholars and industry professionals offer differing conceptualisations without a unified consensus [21; 22]. For example, some view the metaverse primarily from a technological perspective, emphasising its infrastructure and functionalities, while others approach it philosophically, considering its societal implications and user experience [23; 24]. Moreover, the complex nature of defining the metaverse stems from its broad scope, encompassing gaming, social interaction, economics, education, and other domains [25]. The definition of the metaverse is further complicated by its rapid advancement of enabling technologies and the continuous expansion of associated domains [26]. These technologies are essential systems that underpin the creation and functioning of the metaverse, enhancing immersive user experiences that integrate physical and virtual environments [27]. The enabling technologies include artificial intelligence (AI), blockchain, cloud computing, digital twins, and advanced network infrastructure like 5G. Blockchain functions as a decentralised, transparent, traceable, auditable, secure, and trustworthy digital ledger of transactions that can safeguard digital assets in the metaverse [28]. Artificial intelligence provides advanced services, including natural language processing, image recognition, recommendation systems, and virtual customer support, collectively enhancing user experience and interaction efficiency within the metaverse [29; 30].