Final answer:
The z-axis indeed refers to screen depth in a three-dimensional coordinate system, providing the third dimension needed in addition to width (x-axis) and height (y-axis).
Step-by-step explanation:
The statement that the z-axis refers to screen depth is true. In a three-dimensional coordinate system, such as the Cartesian coordinate system, the z-axis is indeed used to represent the third dimension, which is the depth aspect in relation to a two-dimensional plane. While the x-axis and y-axis describe width and height on a flat plane, respectively, the z-axis adds the additional dimension of depth. This allows for a more accurate representation of points in 3-dimensional space. To visualize this, imagine if (x, y) represents a point on a sheet of paper, then (x, y, z) would define the position of a point in the space above or below that paper, with positive z values representing points above the paper and negative z values representing points below it.