Broadly speaking, econometrics aims to give empirical content to economic relations for testing economic theories, forecasting, decision making, and for ex post decision/policy evaluation.

J. Geweke, J. Horowitz, and M.H. Pesaran (2007)

System theory is an interdisciplinary theory about the nature of complex systems in nature, society, and science, and is a framework by which one can investigate and/or describe any group of objects that work together to produce some result.

en.wikipedia.org/wiki/ System_theory