'System' is the concept that refers both to a complex of interdependencies between parts, components, and processes, that involves discernible regularities of relationships, and to a similar type of interdependency between such a complex and its surrounding environment.

Parsons (1968) "Systems Analysis: Social Systems" in: David L. Sills ed. International Encyclopedia of the Social Sciences. p. 458; Cited in: Ida R. Hoos (1972) Systems Analysis in Public Policy: A Critique.