Based on the image, what mathematical concept is being illustrated?

The image illustrates the concept of a function, specifically its graphical representation. The curve shown is the graph of the function y = f(x), plotted against the x and y axes. Various points on the x-axis are labeled as x₁, x₂, x₃, etc., indicating specific input values for the function. The peaks and troughs of the curve represent the output values (y-values) of the function for those input values.