USM = Unsharp Mask, and it is visible under the "sharpen" subset of Photoshop filters. It is the most common way of bumping up the visual acuity ("sharpness") of images on this site. It's a very flexible tool. As others have pointed out, it's also the acronym for Ultrasonic Motor in autofocus lenses.
Spot Editing isn't just one thing, it refers to a class of actions you might take as you edit an image. We have two different rulesets, basic and advanced. In basic editing challenges, "spot editing" is not allowed. The easiest way to visualize spot editing is to realize that it involves any action that is applied to a portion of the image, usually by selection, rather than to the entire image at once. It doesn't have to be a selected portion, though, in the sense that the clone tool or the burn tool (or many other tools) only affect the area to which you apply them, and the "selection" as it were, is made on the fly as you "paint" with these tools.
It is possible to make basic editing-legal local area adjustments by using hue/saturation and selective color adjustment layers. Both of these are Photoshop adjustments the restrict their effects to predefined ranges of the image. You can, for example, legally change the saturation and brightness and even the hue of the blue portions of your image by adjusting the blue slider in hue/saturation, and you can legally change the colors of the dark, middle, and white areas of your image by using selective color adjustment, to name but two examples.
One thing you can't ever do in basic editing is make a "selection", whether by lasso, magic wand, or marquee, and then apply changes to the selected area. You can only do that in advanced editing. You also cannot use layers that contain pixel information, only "adhustment layers" which of themselves have no pixel information contained. And these layers can only be used in "normal" mode, whereas in advanced editing we have a whole list of other modes that allow us to achieve sometimes spectacular results.
Hi rikki11. There are some terrific tutorials under the "Learn" menu heading on dpChallenge. I've gone through every one of them, and learned something each time, even if I thought I already knew how to do something!
