Whenever I look at Aspergers/Autism related forums these days, there are never ending references to the acronym 'ND'.
As a photographer, I find this frustrating, as to me an ND is a Neutral Density filter.
I don't tend to use ND filters in still photography much, but they are pretty much mandatory in video, and video cameras tend to have several built in ND filters, which you can select with a switch.