The S-system, or S-system model, is a mathematical framework used to describe and analyze complex systems in various fields, including biology, economics, and engineering. It focuses on the relationships between different components of a system, allowing researchers to understand how changes in one part can affect the whole. This model is particularly useful for studying dynamic systems, where variables change over time. By using differential equations, the S-system can simulate the behavior of these systems, helping scientists and engineers predict outcomes and optimize performance in real-world applications.