REgression by Bionic turtle.

The residual plot illustrates at least two properties of the classical linear regression model (CLRM):

• The expected (average) residual is zero,
• Homoscedastic residuals; e.g., we don’t expect to see the dispersion of the residuals exhibiting some patter as we move from left to right along the independent variable
• Also, we can visually (sort of) confirm that the residuals are not correlated with the independent variable X. In short, the residual plot should be centered at zero but otherwise without meaningful, obvious pattern (bias)