Thanks for explaining what USM means. My research led me to believe it meant Ultrasonic Motors, and that made absolutely no sense. I was thinking it had something to do with lens adjustment.
Thanks. I hold down the ALT key when adjusting Whites and Blacks. I'll look into tutorial videos for Masking/UnMasking.
I'm not familiar with LR, but I can give some historical information about the term "unsharp mask" (just picking at nits, but the term is not "unsharpen"). The term originated back in the days of black and white photography where the edge contrast of images was enhanced for publication in books and magazines because the process of creating printing plates resulted in lower contrast than the original images. The process basically involved creating a negative mask that was slightly out of focus so that the width of edges was increased. The mask caused the the light side of edges to have increased brightness while the darker side of the edges were made darker. That explains why this sharpening technique has such a strange sounding name that sounds like it contradicts its intent. In reality we can't really sharpen a slightly out of focus edge, but what we can do is create the illusion of a sharper edge by increasing contrast along the edge. In digital photography we have so much more control over applying this technique. We can easily adjust the radius of the edge and the amount of contrast to apply. We can even choose the luminance ranges where USM is applied and we can do selective sharpening by using layers and masks and "painting" in selected parts of the sharpened image while not changing other parts of the image.
I use Adobe Camera Raw for processing my raw images and I'm fairly certain that LR has basically the same controls. The ACR sharpening is basically USM. If I hold down ALT while moving the sliders I am able to clearly see what is being sharpened and by what amount.