nonlinear system
Noun
Meaning
a system whose performance cannot be described by equations of the first degree
Source: WordNetHypernyms
Examples
Of course the word chaos is used in rather a vague sense by a lot of writers, but in physics it means a particular phenomenon, namely that in a nonlinear system the outcome is often indefinitely, arbitrarily sensitive to tiny changes in the initial condition.
Nonlinear signal processing is closely related to nonlinear system identification Billings S.A. "Nonlinear System Identification: NARMAX Methods in the Time, Frequency, and Spatio-Temporal Domains".
Practical considerations The concept of intercept point is based on the assumption of a weakly nonlinear system, meaning that higher-order nonlinear terms are small enough to be negligible.