Learn in the textbookPKI and the Core of Public Key Infrastructure
DefinitionA trust anchor (トラストアンカー) is the starting point that certificate verification is set to trust without checking any further.
ExplanationVerification starts from the received certificate and follows the issuers one by one, confirming that each signature is correct and that no certificate has expired or been revoked; it succeeds once it reaches a point decided in advance as trusted. That predetermined point is the trust anchor, and in most cases a root certificate built into the browser or OS plays this role. Trust flows down from the trust anchor to the certificates below it, so the point where the path ends is where trust starts.
AnalogyFollowing a stranger's chain of letters of introduction, if you finally reach the name of a mentor you know well, you can trust the introduction. The mentor is the trust anchor.
Memory hookAn anchor holds a ship in place: the step-by-step check stops here and settles instead of drifting.