Philosophy of Nudism and Naturism

I came across this passage from Muir where he is obviously skinny dipping up in Yosemite somewhere near half dome. No pain here, no dull empty hours, no fear of the past, no fear of the future. These blessed mountains are so compactly filled with...

UF Study bares contradictions about American nudists a University of Florida study by Ellen Woodall "It seems clear that social class distinctions are not only visible, but (are) sustained by the practice of nude recreation," Woodall...

Probably the most important question what is or is not nudism? Is exhibitionist the same as nudism? Is nudism tied to sex? Is swinging a part of the nudist lifestyle?