Pearson's correlation coefficient is a measure of the linearity of a line on a scatterplot. It is commonly denoted by r and is used to measure the correlation of data between two variables, one independent (plotted on the X axis) and one dependent variable (plotted on the Y axis)

ie. Annual Salary depends on Age. Therefore, the first stated variable is the dependent variable and is plotted on the Y axis (Annual Salary), while the second variable is the independent variable and is plotted on the X axis