| set of interrelated items that collectively fulfil a requirement
Note 1 to entry: A system is considered to have a defined real or abstract boundary.
Note 2 to entry: External resources (from outside the system boundary) may be required for the system to operate.
Note 3 to entry: A system structure may be hierarchical, e.g. system, subsystem, component, etc.
Note 4 to entry: Conditions of use and maintenance should be expressed or implied within the requirement.