I do have one little twist, and that is that a complex system is one in which you can use mathematical modeling to better understand it. This leads me nicely to my second lecture: what is mathematical modeling? This question I have thought about a lot, and I think here I give a reasonably useful and general explanation of why we use mathematical models. Models are used for one of four reasons:
1, Explain data as simply as possible.
2, Link together levels of explanation.
3, To provide detailed descriptions.
4, To predict future outcomes.
Complex systems are most associated with number 2. Have a look at the video and see what you think.