Image Geometry is the combination of Image Cropping -- whether the image fills your screen from top to bottom and left to right, and with no pixels lost off any side -- and Aspect Ratio -- whether circles in the content actually look like circles on your screen, instead of tall ovals or wide ovals.

If your video setup has a problem with Aspect Ratio, you will likely notice it pretty quickly.  Indeed you may even have CHOSEN to use incorrect Aspect Ratio -- typically because you don't want to see Pillar Box Bars or Letter Box Bars padding the image on your screen.

But Image Cropping problems can be subtle.  And getting them wrong can have a surprisingly large effect on image quality!