So, what is a system? A system is a set of things-people, cells, molecules, or whatever-interconnected in such a way that they produce their own pattern of behavior over time. The system may be buffeted,constricted, triggered, or driven by outside forces. But the system's response to these forces is characteristic of itself, and that response is seldom simple in the real world.
Donella H. Meadows. Thinking in Systems: A Primer (Kindle Locations 89-90). Kindle Edition.
This is one of the most important books I've ever read, if you want the way you think about the world to change read it. It's a very short read to.
Yes. So it is systems theory applied in multiple domains, can be used as a framework to understand or model the world around you.
See my other posts.
It is a way of thinking about the world, and contrasts with traditional linear thinking. It is where interaction and interrelationships are understood to drive outcomes and behaviours of the system under study.
Systems Thinking redirects to Systems Theory on wikipedia: https://en.wikipedia.org/wiki/Systems_theory
Is that what we're talking about?