This Technical Specification provides a set of core terms and associated definitions to reflect the basic concepts used in the metaverse. The document aims to encourage a mutual and consistent understanding of, and a coherent approach to, activities relating to the metaverse, and the use of harmonized terminology. It includes terms and definitions for the metaverse, which have been widely used in the FG-MV deliverables, including terms already defined in relevant standards development organizations (SDOs). This document is intended to be relevant for: a) people engaged in metaverse activities; b) people involved in metaverse activities at ISO, IEC, ITU-T, and other international standards bodies; and c) developers of national or sector-specific standards, guides, procedures, and codes of practice relating to the metaverse.