The deviation from linearity in an electronic circuit, an electro-optic device or a fiber that generates undesired components in a signal Examples of fiber nonlinearities include SBS, SRS, FWM, SPM, XPM, and Intermodulation
The interactions of agents that produce aggregate behavior are nonlinear in that you cannot derive that behavior by adding up the individual agent behavior or interactions The sum is greater than the parts
In neural networks, nonlinearity can take several forms/feedback into the same layer, multi-layer feedback, normalization and competition, or multi-layer feed-forward networks which use non-linear transfer functions
The deviation from a best fit straight line of true output vs actual value being measured
What goes into a system comes out changed by its passage through that system-in other words, distorted The ideal of an audio component and an audio system is to be linear, or nondistorting, with the image on one side of the mirror identical to the image on the other side