> For the complete documentation index, see [llms.txt](https://docs.empe.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.empe.io/develop/verifier/terminology-and-concepts.md).

# Terminology and Concepts

This glossary defines the terms used throughout the Verifier documentation.

* **Self-Sovereign Identity (SSI)**: A user-centric approach to digital identity, allowing individuals and organizations to control their identifiers and credentials without centralized authorities.
* **Decentralized Identifier (DID)**: A unique identifier whose DID Document (public keys and service endpoints) can be resolved to establish trust. In this system, DIDs are either `did:web` (resolved over HTTPS at a domain) or `did:key` (self-contained — the public key is encoded directly in the identifier). A verifier signs its authorization requests with one of these DIDs so that wallets can verify the request originates from a known party.
* **Verifiable Credential (VC)**: A cryptographically signed credential that attests to certain attributes of an entity. VCs follow W3C standards, ensuring integrity and authenticity.
* **Verifiable Presentation (VP)**: A presentation of one or more VCs by a holder to a verifier. The VP proves possession and authenticity of the credentials without revealing unnecessary information.
* **Credential formats**: The Verifier accepts two credential formats: **SD-JWT VC** (`dc+sd-jwt`), which supports **selective disclosure** so a holder can reveal only the claims a verifier needs, and **JWT-VC-JSON** (`jwt_vc_json`), a JWT-based W3C credential.
* **OpenID4VP (OpenID for Verifiable Presentations)**: The protocol the Verifier uses to request, receive, and validate presentations. You create an authorization request, the holder's wallet returns a presentation, and the Verifier validates it. Supported draft versions are `v1`, `v1.draft21`, and `v1.draft24`.
* **Verification queries (DCQL / Presentation Exchange)**: The two ways to express which credentials and which fields a presentation must contain. **DCQL** (Digital Credentials Query Language) and **DIF Presentation Exchange v2** are both supported — each authorization request carries exactly one of them. They act as structured filters, ensuring that only credentials meeting the defined criteria are accepted.
* **EMPE DID method / EMPE blockchain**: An on-chain DID method in the wider Empeiria EVDI ecosystem. The Verifier resolves `did:web`, `did:key`, and `did:jwk` directly; `did:empe` resolution is an ecosystem roadmap item (see [Future Enhancements](/develop/verifier/future-enhancements.md)).


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