Wiktionary
n. A mathematical model of a system based on the use of a linear operator.
Wikipedia
A linear system is a mathematical model of a system based on the use of a linear operator. Linear systems typically exhibit features and properties that are much simpler than the nonlinear case. As a mathematical abstraction or idealization, linear systems find important applications in automatic control theory, signal processing, and telecommunications. For example, the propagation medium for wireless communication systems can often be modeled by linear systems.
Usage examples of "linear system".
Apparently you can go many millions of times the speed of light with the linear system but not even Perry Rhodan has put it to the test so far.
Marx's predictions were based on the assumption that history is a linear system, and using those assumptions he predicted the future.
Being now satisfied that the linear system is not applicable to the present case, we shall return to circularity.
A non-linear system turned ninety degrees and mapped out in three dimensions.
Like the determinant of a linear system under orthogonal rotation, or the Newtonian equations of motion with a Galilean transformation, or Maxwell's equations with a Lorentz transformation.