The "y-value" refers to the vertical coordinate in a two-dimensional graph, typically represented as part of an ordered pair x, y. In this context, the x value indicates the horizontal position, while the y value shows how high or low a point is on the graph. This is essential for plotting points and understanding relationships between variables in mathematics. In the context of functions, the y-value is the output of a function for a given input x-value. For example, in the function y = 2x + 3, if you substitute x with 1, the y-value would be 5. This relationship helps visualize how changes in one variable affect another.