SCAS is an acronym for "System for Cross-domain Identity Management" which refers to an open standard for securely exchanging user authentication and authorization data across multiple domains. Synonyms for SCAS include cross-domain authentication, single sign-on (SSO), and federated identity management. These terms all refer to the concept of providing users with a single set of login credentials that can be used to access multiple applications and services across different domains. Other related terms include identity federation, identity bridge, and identity broker. In summary, SCAS and its synonyms are all related to the important task of securely managing user identities and access across multiple systems and domains.