Usually regarding P. subfusca. Some people think that there are two different forms(high/low), and others think that they are just trippin'. Some do appear slightly different, but taxonomists still classify them as the same spider.
I won't even begin to give my opinions on this, as taxonomy is way above my skill level. I have seen subfuscas that do look a lil different, but I've also seen alot of species that vary slightly between each individual.
Use the search function to find alot of heated arguments over this topic. You would swear they were debating abortion or something lol, they get really into it.
In this particular instance "Highland" would be the montane (mountain form) while "Lowland" would be from the lower elevations of the same general area. You may run across the term in other threads on occassion.