A system is a structure of interconnected parts. It can only function when its constituents are linked with each other, when they work together to achieve a specific outcome.
It follows, that society could be described as a system that is built on a (conscious/unconscious, voluntary/involuntary) community of people.
In her book, Thinking in Systems, Donella H. Meadows defines a system as “an interconnected set of elements that is coherently organized in a way that achieves something.” In other words, systems have parts that work together that make things happen. Conversely, when the parts no longer work together, and thus no longer make things happen, the system is no longer a system.