Look up the word resolution in a good dictionary. You can't completely decouple pixel density from resolution in the context talking about the resolution of a LCD panel. Resolution is more than simply the number of horizontal and vertical pixels. Either also have to factor in the panel's size or dpi ( two ways of getting to the same issue).
For the common distance usagae for a Pixel or Apple retina offering dpi is a factor in resolution in any real sense of the word.
Si tacuisses, philosophus mansisses.