When you have a printed circuit board (PCB) made you can have markings and labels put on the board using screen printing. This labeling is often just referred to as the silkscreen. However the methods of silkscreen labeling are generally not as sharp as the photo-imaging methods used to pattern the solder mask. For this reason I generally like to use the solder mask layer for labeling more than the silkscreen layer. That being said, on the last batch of LCD charger boards the solder mask looked awful! This is definitely not the norm, but it made me think that I should really change the way I do labeling so that it is not so dependent on the quality of the solder mask. My solution came from the fact that the etching of the copper is the most precise (it's an actual spec you pay for). Now the copper defines the edges and the sharpness of the label is no longer dependent on the quality of the solder mask (or silk screen for that matter).