Past the elastic deformation region / yield stress you get plastic deformation, which even when the stress is completely removed there is permanent deformation.
P is the Proportional Limit, where it stops being linear, but remains elastic for a short while longer, meaning any deformation can still be recovered. E is the Elastic Limit, where it changes from elastic to plastic
Everything past the dotted line is the point where the material won't go back to its original shape.
Example: You can push on the hood of your car all you want, it'll flex, and go back to its original shape (elastic deformation); but stand on it, and it'll dent (plastic deformation).