A graph of the observed (actual) response values versus the predicted response values. It helps to detect observations that are not well predicted by the model.
The difference between this graph and the one seen in Diagnostics is that models with transformations can be displayed in original scale.
This will usually result in more points towards the lower left than what is shown on the diagnostics version.
The data points should be split evenly by the 45 degree line in either scale.