Definition(s)
Security Perimeter
Boundary (logical or physical) of the domain in which a security policy or security architecture applies, i.e., the boundary of the space in which security services protect system resources [11].
Source: ANSI/ISA–99.00.01–2007, Security for Industrial Automation and Control Systems, Part 1: Terminology, Concepts, and Models, 29 October 2007. National Standard