Which of the following best describes a linear function?

A linear function is best described as a function that graphs as a straight line. This characteristic of linear functions is derived from their standard form, which is typically written as (y = mx + b), where (m) represents the slope and (b) the y-intercept. Because of this linearity, the graph of such a function will always produce a straight line when plotted on a coordinate plane.

In contrast, a function with a quadratic equation will graph as a parabola, which is distinctly non-linear due to its curvature. Functions that oscillate between different values are periodic, such as sine or cosine functions, and do not display a linear relationship, instead offering a wave-like graph. Lastly, functions defined by a polynomial of degree three or higher are classified as cubic or higher-degree polynomials, and they can exhibit intricate behaviors, such as multiple turning points and inflection points, rather than representing a straightforward slope associated with linear functions. Thus, the defining characteristic of a linear function is its ability to produce a straight line when graphed, reinforcing the correctness of the chosen answer.