1. An area of responsibility for the security of a system as defined in a System Security policy. Note: The terms Global Security Environment (GSE), Local Security Environment (LSE) and Electronic Security Environment (ESE) are used to categorize security domains [CESG]. 2. A bounded group of security objects and security subjects to which applies a single security policy executed by a single security administrator [ECMATR46]. 3. A set of entities that is subject to a given security policy and a single security administration [ECMA138]. 4. A set of elements, a security policy, a security authority and a set of security relevant activities in which the set of elements are subject to the security policy, administered by the security authority, for the specified activities [10181-1]. 5. A complete set of objects, subjects and policies which determine the local definition of “security” [POSIX.6].