Policies that govern how entities in differing domains honor each other’s authorizations. An authority may be completely trusted—for example, any statement from the authority will be accepted as a basis for action—or there may be limited trust, in which case only statements in a specific range are accepted.
Sources:
NIST SP 800-95
under Trust Relationships
from
Open Grid Services Architecture Glossary of Terms
An agreed upon relationship between two or more system elements that is governed by criteria for secure interaction, behavior, and outcomes relative to the protection of assets.
Sources:
NIST SP 800-160v1r1
The access relationship that is granted by an authorized key in an account on one system (server) and a corresponding identity key in an account on another system (client). Once deployed, these two keys establish a persistent trust relationship between the two accounts/systems that enables ongoing access.
Sources:
NISTIR 7966
under Trust Relationship