Several sets of (x, y) points, with the correlation coefficient of x and y for each set. Note that the correlation reflects the non-linearity and direction of a linear relationship (top row), but not the slope of that relationship (middle), nor many aspects of nonlinear relationships (bottom). N.B.: the figure in the center has a slope of 0 but in that case the correlation coefficient is undefined because the variance of Y is zero.
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