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Systems thinking is the process of understanding how things, regarded as systems, influence one another within a whole.
https://en.wikiquote.org/wiki/Systems_thinking
Systems Thinking is a ??? of Systems Theory, which is the interdisciplinary study of systems. A system is a cohesive conglomeration of interrelated and interdependent parts which can be natural or human-made. Every system is bounded by space and time, influenced by its environment, defined by its structure and purpose, and expressed through its functioning. A system may be more than the sum of its parts if it expresses synergy or emergent behavior.
https://en.wikipedia.org/wiki/Systems_theory
Systems may be nested, whereby a system component may itself be a system.