access control function

A capability or software mechanism, within a system or application, whose specific role is to evaluate a subject's credentials or authorizations and enforce a policy decision — granting or denying the requested access to a resource, service, or operation. It is the operative unit that translates an access-control policy into a runtime enforcement action, distinct from the broader policy, model, or administrative process that surrounds it. In standards and legal instruments — including ITU-T security definitions and computer-crime law — the term names this enforcement function as a discrete, identifiable component: the part of a system that checks an identity code and removes or maintains restrictions on a protected use.