The word linear means something having to do with a line. Tending to jump back and forth. The graph of a linear function is a line.
Instead it makes sudden changes or seems to develop in different directions at the same time.
Nonlinearity is a mathematical term describing a situation where the relationship between an independent variable and a dependent variable is not predictable from a straight line. Therefore they have the opposite properties of a linear function. Large deformations material nonlinearitys ie. Math teacher Bon Crowder shows some examples of what a non-linear equation means in math t.