What is the name of the vertical number line that, along with the x-axis, establishes the coordinate plane?

The vertical number line that, together with the horizontal x-axis, creates the coordinate plane is called the y-axis. The y-axis is used to plot the vertical position of points in relation to their horizontal position along the x-axis, allowing you to determine the location of any point in a two-dimensional space.

In a standard Cartesian coordinate system, the intersection of the x-axis and the y-axis is known as the origin, which represents the point (0, 0). The x-axis is the horizontal line, while the quadrants are the four sections formed in the coordinate plane by the intersection of these two axes. Understanding the role of the y-axis is fundamental to graphing and analyzing relationships between variables on a coordinate plane.