What are the roles issuer, holder and verifier in SSI, and what else can "verifier" mean?

The issuer verifies claims about subjects or objects and issues verifiable credentials that the holder may voluntarily take into its wallet; the holder stores VCs in a decentralised store it controls and presents them or parts of them; the verifier checks the integrity, validity and ideally the authorship of received VCs or VPs.

* Issuer, holder and verifier, with the verifiable data registry as the shared trust anchor. *

"Verifier" has a second, classical meaning: the part of an IdP or RP that authenticates the subject with its authentication service by matching the authenticator's output against stored credentials. Synonyms: Aussteller, Inhaber/Halter, prüfende Instanz.

Go deeper:

• W3C Verifiable Credentials Data Model v2.0 — the standard for credentials, presentations and the issuer-holder-verifier ecosystem.