It's possible to partially select the pixels, thereby reducing the effect of your edits. The effect is similar to lowering the opacity of a layer, but the semi-opacity is built into the selection itself. The edges of any selection can be softened, or made to gradually increase in transparency. When you apply a command, soft edges result in a smoother transition between the selected and unselected pixels. Increase the width of the transition by applying a feather value.
Gray pixels result in partial selections.
Quick Mask selections. Using a soft brush or applying a blur filter to a selection in Quick Mask mode results in feathered edges. Lowering the opacity of a brush results in a partial selection. The remaining values result in partial selections. As long as a floating selection remains active, it exists as a separate item in the Layers Palette.