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Setting terms and definitions in any area is a difficult undertaking, but when the area is as broad as multidisciplinary as the Metaverse and covers so many different fields, the undertaking is not just difficult but unrewarding: too many fields address the same notion with different terms and sometimes the same terms in different fields have different meanings.

The drafting of this document has faced two options in developing terms and definitions: a balkanised terminology leading to a Tower of Babel but not displeasing anyone or a unified terminology serving the purpose of the MMM but displeasing most. This document has selected the latter, no matter how unrewarding it may be. The intention is to facilitate the creation of a common language across industries and application domains in the context of the Metaverse.

Terms are organised in 3 Tables: Table 1 collects the Definitions of the Terms used in this document with the exception of those defined in Table 2 (Data Types) and Table 3 (Actions).

A dash “-” preceding a Term in Table 1 means the following:

  1. If the font is normal, the Term in the table without a dash and preceding the one with a dash should be placed before that Term. The notation is used to concentrate in one place all the Terms that are composed of, e.g., the word Decentralised followed by one of the words Application, Autonomous Organisation, Finance, System, and User Identifier.
  2. If the font is italic, the Term in the table without a dash and preceding the one with a dash should be placed after that Term. The notation is used to concentrate in one place all the Terms that are composed of, e.g., the word Interface preceded by one of the words Brain-Computer, Haptic, Speech, and Visual.

Table 1 – General Terms and Definitions

Terms Definitions
Action An operation affecting User, Entity, Asset, Device, Service, and User.
Avatar A rendered Digital Human.
Blockchain A shared immutable ledger stored on a peer-to-peer network of computers.
Common Metaverse Specifications (CMS) The collection of standards specifying the technologies enabling Metaverse Interoperability including recognised Profiles.
Connected Autonomous Vehicle (CAV) A vehicle able to autonomously reach a geographical position by using its own sensing, processing, and actuation capabilities and by exchanging information with other CAVs.
Data Information represented in digital form.
–          Format The syntax and semantics of Data.
–          Type Data characterised by its Format.
–          Application (dApp) A Process that runs on a decentra­lised computing system.
–          Autonomous Organisation (DAO) An organisation without centralised leadership, where the main governing rules are typically encoded by means of a Smart Contract.
–          Finance (DeFi) A financial technology based on a secure infrastructure of distributed ledgers like those used by crypto currencies.
–          System A set of dApps enabling a group of Users to make decisions without a centralised entity.
Device Equipment used to Sense and/or Actuate a Universe Environment allowing:

–          A Universe Environment to interact with a Metaverse Instance or

–          A Metaverse Instance to interact with a Universe Environment.

Duty A moral or legal obligation to act or behave.
Entitlement The state of a User having certain Rights in a Metaverse Instance.
Functionality An attribute of a Metaverse Instance expected to be enabled by a Common Metaverse Specifications Tool.
–          Digital Either a Digitised or a Virtual Human.
–          Digitised The digital representation of a human.
–          Virtual A computer-created Object that has a human appearance when rendered but is not a Digitised Human.
Governance The action or manner of directing and controlling entities of the Metaverse Ecosystem.
Information and Communication Technologies (ICT) Technologies that enable the processing and distribution of information via the network.
Interface A communication pathway enabling systems to interact.
–          Brain-Computer (BCI) A communication pathway that allows a human to interact with a Metaverse Instance by sensing and processing the electrical activity of the brain.
–          Haptic A communication pathway that allows a human to interact with a Metaverse Instance through bodily movements and sensations.
–          Speech A communication pathway that allows a human to interact with a Metaverse Instance using spoken language.
–          Visual A communication pathway that allows a human to interact with a Metaverse Instance through bodily movements and visual messages.
Interoperability The ability of a Metaverse Instance to exchange and make use of Data from another Metaverse Instance.
Metadata An attribute of Data, e.g., of a User, an Environment, an Object, or a Service.
Metaverse A collection of digital environments that are implementations of Common Metaverse Specification Profiles; it is populated by Digital Objects that are representations of either real Objects – called Digitised – or computer-generated Objects – called Virtual – or both.
–          Actuator A Device able to Render Data from a Metaverse Instance in a Metaverse Environment.
–          Ecosystem The ensemble of entities and rules ensuring that Metaverse Instances operate in the interest of Metaverse Stakeholders.
–          Enabling Service Layer The set of Services such as payment, security, identity, privacy, etc. that enable operation of a Metaverse Instance.
–          Environment A portion of a Metaverse Instance.
–          Experience Layer The set of functions, such as Devices, that generate Experiences.
–          Functionality The ability of a Metaverse Instance to perform actions tthat further the goals set by the Metaverse Manager for the Metaverse Instance.
–          Industry The collection of players that support the design, deve­lopment, deployment, operation, and content and service provisioning to Metaverse Instances.
–          Instance An implementation providing all or a subset of Functionalities.
–          Infrastructure Layer The set of functions such as network, transport, storage, and (cloud, edge) processing that enable a Metaverse Instance to operate.
–          Operator A User engaged in activities using Services a Metaverse Instance (e.g., a vendor, a service provider)
–          Partner A User participating in activities of a Metaverse Operator (i.e., the business customer of an Operator)
–          Platform Layer The set of Services, such as content creation, content discovery, and content access functions that enable a Metaverse Instance to operate.
–          Process The instance of a program being executed.
–          Profile A recognised subset of the Functionalities (Functionality Profile) or Technologies (Technology Profile) specified by the Common Metaverse Specifications.
–          Sensor A Device able to inject Data into a Metaverse Environment.
–          Service A Functionality that enables a User to perform a particular Action in a Metaverse Instance or Environment.
–          Specifications (CMS) A collection of standards specifying the technologies enabling Metaverse Interoperability.
–          Stakeholder An entity or a human performing a function aimed at achieving a goal in a Metaverse Instance.
–          State The set of values and stored data of a Metaverse Instance at a given time.
–          Tool A Technology or group of Technologies enabling a Metaverse Instance to provide a Functionality.
–          Technology A structured application of scientific and/or technical methods that supports a Functionality.
–          Audio The digital representation of an object or a computer-generated Object that can be rendered to and perceived by a human ear.
–          Autonomous A Virtual Object with the ability to act (e.g., move, speak, respond, execute) with a degree of autonomy.
–          Composite An Object that includes more than one Object Type.
–          Digital A Digitised or a Virtual Object.
–          Digitised The digital representation of an object.
–          Haptic An Object with the haptic features of an object able to be rendered to provide haptic sensations in a human.
–          Human An Object representing a human.
–          Speech The digital representation of a sound emitted by the vocal tract of a human or generated by a computer with similar audio characteristics.
–          Type One of Audio, Visual, Haptic, Olfaction, and Gustation.
–          Virtual A computer-generated Object that is not a Digitised Object.
–          Visual The digital representation of an object captured by an electromagnetic or high-frequency audio signal or a computer-generated or that can be rendered to and perceived by a human eye.
Oracle A Service providing information from a Universe Environment to a Blockchain.
Privacy The Rights of a User to keep their personal data secret.
–          Functional The grouping of Functionalities offered by a Metaverse Profile.
–          Technology The grouping of Technologies offered by a Metaverse Profile.
Representation Data that represent an entity of a Universe Environment in a Metaverse Instance.
Sense of
–          Agency The subjective awareness of being able to decide, execute, and control one’s own actions in a Metaverse Environment.
–          Embodiment The engagement of senses to form a complete Environment Experience.
–          Presence The feeling of being in a Metaverse Environment with other Digital Humans for real.
Smart Contract A Program stored on a Blockchain that runs when activated by an external entity, e.g., a User or another Smart Contract.
–          Fungible A representation of an Asset that is interchangeable with other Assets of the same type.
–          Non-Fungible (NFT) A unique digital identifier of an Asset that:

–          Cannot be copied (i.e., a copy is known to be a copy), substituted, or subdivided.

–          Is recorded in a digital ledger.

–          Is used to certify Object authenticity and ownership.

Trust-less system A system allowing a User to make reliable Transactions without trusting or knowing the parties the User makes Transactions with.
Universe The physical world.
Use Case A particular example of the use of a Metaverse Instance in an application domain.
–          Keys The pair of public and private keys where the public key is used to encrypt, and the private key is used to both encrypt and decrypt Data.
User Identifier
–          Decentralised An Identifier that enables the verifiable association with a User without requiring a centralised registry.
–          Self-Sovereign A Decentralised Identifier derived from the User’s Public Key owned and managed directly by the User based on the knowledge of their own Private Key, e.g., stored in the Crypto Wallet enabled by the Blockchain underpinning the Metaverse Instance.
–          Crypto Software or hardware holding the Public and Private Keys of a User to enable them to make Transactions by accessing their Account on a Blockchain.

Table 2 – Definitions of Data Types

Terms Definitions
Account A dataset that unequivocally identifies a User. A User may have more than one Account.
Address A URL.
Amount The expression of a Value in a Currency.
Asset An Entity with associated Rights.
Cognitive State The representation of a User’s Personal Status that reflects the way they understand the Environment, such as “Confused”, “Dubious”, “Convinced”.
Currency A medium of exchange enabling Transactions in a Metaverse Instance.
Emotion The representation of a User’s Personal Status that results from their interaction with an Environment, such as “Angry”, “Sad”, “Determined”.
Entity Any of Environment, Event, Experience, Object, Scene, or Stream.
Environment A portion of a Metaverse Instance for which an Account holds.
Event The Data of the recording of a Location, its Objects and their Animations starting from Start Time until End Time.
Experience The Data perceived by and the Interactions of a User with the Entities of an Event.
Identifier Data establishing an association with a single instance of a Data Type. An identifiable Entity may be Identified by more than one Identifier.
Location An Identifiable portion of a Metaverse Environment.
Metadata Attributes of Data, e.g., of a User, an Environment, an Object, or a Service.
Object Data that can be used by a Process or Service, e.g., animated and rendered to cause an Experience.
Object Model An Object representing the features of an object that can be Animated by a Stream.
Orientation The set of the 3 roll, pitch, yaw angles of the principal axis (x) of a Rendered Object, its y axis (right-to-left) and its z axis (pointing up).
Persona The Model of a Digital Human.
Personal Status The representation of the information internal to a User characterising their behaviour.
Point of View The Spatial Attitude of a Digital Human watching the Environment.
Position The x,y,z coordinates of an Object with respect to a Cartesiam set of coordinates in a Metaverse Environment.
Provenance The Transactions executed on an Asset starting from the first and including the last.
Rights Data expressing the ability of a User to perform an Action on an Asset in a Metaverse Instance or Environment.
Scene A dynamic composition of Objects described by Time and Spatial Attitudes.
Social Attitude The representation of a User’s Personal Status related to the way the User intends to position vis-à-vis a Metaverse Environment, e.g., “Respectful”, “Confrontational”, “Soothing”.
Social Graph Data representing the network of connections of a User with Users, Entities, Locations, and Services.
Spatial Attitude The Position and Orientation of an Entity, and their derivatives up to the second order.
Stream A continuous flow of Data from a Device or Location to another Device or Location.
Terms of Service Data expressing the terms under which a User operates in a Metaverse Instance or Environment and the obligations undertaken by them.
Time Data represented by YYYY/MM/DDThh:mm:ss.SSS. Any of Y, M, D, h, m, s, and S are represented by a decimal digit. T is a separator.
Transaction The operation that changes the state of the Account of one or more Users and potentially of the Service enabling the Transaction.
User Either a Digitised Human driven by a human, or else a Virtual Human driven by a Process.
User Data Data generated by a User while in a Metaverse Environment.
User Profile Data associated with a Metaverse User.
Value The decimal number expressing the Currency units of an Amount.
Wallet A container of Currency units.

Table 3 – Definitions of Actions

Terms Definitions
Actuate Stream an Entity from a Location to a Device.
Animate Change the features and/or Spatial Attitude of an Entity by applying a Stream.
Authenticate Determine whether a Device, a User or an Entity is what it states it is.
Ban Disable the Account of a User.
Compose Combine different Entities with their Spatial Attitudes into a Scene.
Create Open an Entity creation session.
Destroy Erase an Entity.
Discover Describe the types and the range of the Entities to be searched and receive Entities satisfying the search criteria, if requested by User.
Edit Modify the Metadata of an Entity.
Instantiate Make an Entity available for further Actions.
Interact Act on a Metaverse Environment and receive stimuli.
Interpret Request and receive information about an Entity or a User.
Move Stream an Entity from Location1 to Location2.
Post Set or modify Asset-related Metadata to an Entity, and optionally submit an Asset to a Marketplace.
Register Open an Account with a Metaverse Instance or Environment.
Remove Take out an Entity from a Location.
Render Make perceptible an Entity and surrounding Objects at a Location.
Select Single out Objects from an Entity.
Sense Stream from a Device to a Location.
Store Store an Entity at an Address.
Stream Send a continuous stream of Data from/to a Location/Device
Transact Decrease Wallet1 by an Amount, increase Wallet2 by a possibly different Amount, and assign Rights to the holder of Wallet1.

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