Definition of Nonlinear system:
System in which (as opposed to linear systems) the effect of external factors is not purely additive, and may even be disruptive. Nonlinear systems cannot be decomposed into parts and reassembled into the same thing, and do not change in proportion to a change in an input. Most economic and social (and many industrial) processes are nonlinear where mathematical analysis (with few exceptions) is unable to provide general solutions.
Meaning of Nonlinear system & Nonlinear system Definition