The Metaverse is an emerging paradigm that integrates immersive digital technologies to create a unified, persistent, and interconnected 3D virtual space with transformative potential across work, education, healthcare, and daily life. This paper presents a comprehensive review of the Metaverse, covering its historical evolution, core characteristics, architectural frameworks, key enabling technologies, standardization efforts, and open challenges. We propose a tripartite architecture comprising infrastructure, interactivity, and ecosystem layers, and provide a structured overview of relevant standards including IEEE 2888, IEEE P2048, IEEE P7016, and ISO/IEC 23005. Seven essential technologi... More >