A document that regulates the security aspects of a proposed link between an agency and an external system. It regulates the security interface between two arbitrary systems operating under two different authorities. It contains a wide range of descriptive, technical, procedural and planning information. Generally, it is preceded by a formal MOA/MOU that defines higher roles and responsibilities in managing an inter-domain link. Source (s): CNSSI 4009-2015 In this manual, an agreement is reached between organizations that own and operate connected computer systems to document the technical requirements of interconnection. The ISA also supports a Memorandum of Understanding or Agreement (MOU/A) between the organizations. Source: NIST SP 800-47 as part of the Interconnection Security Agreement (ISA) Comments on the presentation and functionality of the glossary should be sent to secglossary@nist.gov. Comments on certain definitions should be sent to the authors of the related source publication. For NIST publications, there is usually an email in the document.