Override
You can override settings like verbose messages, image size or render quality (AntiAliasing).
It will trigger different commandline flags that are set in the render config of the render application you use.
So you can have for example set a resoltion of FULL HD (1920x1080) in your scene, but render a small PAL quicktime version of it.
(Or render both without changing anything in your scene)
Note that not all applications support these features (yet)
Render Verbose
Select one of the verbose levels defined in the render config of the app.
Override Image Width/Height
Overrides the image size / resolution of the rendered image.
Render Quality - deprecated
With this setting you can choose render quality settings as they have been defined in the RR render config files for an application.
But as every scene might require different settings, it was replaced by "AA Samples":
AA samples
Change the Anti Aliasing quality relative to the original AntiAliasing quality.