You've been at Nikonians for nearly 10 years. I'm surprised you have missed this.
In any case, I got 17,900 hits on Google for "Photographic Dynamic Range". This was on the first page: Photographic Dynamic Range This idea is similar to DxOMark Landscape DR. Theirs came a year later.
I also got 1,561 hits on NikoScope. Another definition, right here at Nikonians, would be in the third paragraph here: IQ - Image Quality