New word for me but not a new concept. We used to call that out-of-focusness. I have read a lot how some lenses seem to have better "bokeh" than others and I am not sure what they really mean. If I took a group of lenses (multiple brands), primes and zooms, all set at the same focal length and aperture, and photographed a subject from the same distance would not the out-of-focus parts all look the same? If not, why not? These lenses would all be mounted to the same camera so the format size would not be a factor.