trust domain

Definition

A trust domain is the ecosystem of interactions that rely on a trust basis. A trust basis binds controllers, identifiers, and key-pairs. For example the Facebook ecosystem of social interactions is a trust domain that relies on Facebook’s identity system of usernames and passwords as its trust basis.
(Source whitepaper)

Broader definition

A trust domain is a domain that the system trusts to authenticate users. In other words, if a user or application is authenticated by a trusted domain, this authentication is accepted by all domains that trust the authenticating domain.

Domain name

A more technical meaning of 'domain' is on the internet: domain name.