Nonlinear modeling refers to the use of mathematical models that do not follow a linear relationship between variables. In this type of modeling, the relationship between variables is often complex and may involve interactions, feedback loops, or non-linear transformations. Nonlinear models are used in various fields such as economics, biology, physics, and engineering to study systems that exhibit non-linear behavior. Researchers in this area develop and analyze models that can capture the dynamics of these complex systems to make predictions or understand their behavior. Techniques used in nonlinear modeling include differential equations, chaos theory, neural networks, and machine learning algorithms.