This chapter of the book The Metaverse: A Critical Assessment aims to answer the question what the metaverse is or could be. It first investigates this question through a history of the metaverse as an evolving concept and ongoing technological pursuit. Next, it explores the concept of the metaverse through key characteristics, such as immersiveness, persistence, interoperability, and multifunctionality, examining what they entail and how essential they are to defining the metaverse. Third, it examines the key enabling technologies driving its development and use, including virtual and augmented reality, 3D modeling and animation, artificial intelligence, blockchain, Internet of Things and foundational infrastructure systems. The chapter concludes by proposing a definition of the metaverse, informed by the preceding discussion, while recognizing ongoing ambiguities in the terminology.