System: "A set of components that are related in some manner. A set of variables selected by an observer (Ashby, 1960)."
Components which work together in order to form a machine/object/other with the whole greater than the sum of its parts.
Much like in Communication and teamwork studies, the concept of holism is very important in the definition of a system. Everyone might have their own ideas and thoughts about what could make up a system, however it usually revolves around holism.
Emergence: Systems evolve and EMERGE from simple interactions.
From what I can tell, it sounds like this could be difficult to recreate within a mechanical system. I believe an organic system might be the main source of such a concept, because organic creatures are unable to do the same thing every time.
Complexity: A product and descriptor of a system that can be seen as unpredictable and erratic, but not without purpose.
I'm having trouble describing complexity as even the definition seems unsure as to what it is. I'm going to need examples in order to get a better idea as to what makes a system complex