nonlinear

A relationship between two or more variables that can't be represented solely through addition and multiplication. A linear relationship can be represented as a line; a nonlinear relationship can't be represented as a line. For example, consider two models that each relate a single feature to a single label. The model on the left is linear and the model on the right is nonlinear: See Neural networks: Nodes and hidden layers in Machine Learning Crash Course to experiment with different kinds of nonlinear functions.

Practitioners refer to nonlinear when building, training, or evaluating machine learning systems. It appears in research papers, product documentation, and technical discussions about AI capabilities and limitations.