A simple graph usually shows the relationship between two numbers or measurements in the form of a grid. If this is a "rectangular graph" using Cartesian coordinate system, the two measurements will be arranged into two different lines at right angle to one another. One of these lines will be going up (the "vertical" axis). The other one will be going right (the "horizontal" axis). These lines (or "axes", the plural of axis) meet at their ends in the lower left corner of the graph.