Technique used in painting. Primarily employed in painting miniatures or any other medium involving raised surfaces. To drybrush, one first removes the majority of paint from the brush by scrubbing it up and down on old newspaper (that's my own individual twist) and then slowly and gently brushing across the area you wish to paint. Because only a little paint is on the brush, only the raised surfaces will be painted. If you drybrush in a lighter shade of the same colour used on the base coat, this will create highlights, adding depth to the object and making it appear more realistic.
I came across drybrushing through Games Workshop. In my experience, effective use of drybrushing to give an impression of depth can elevate your standard of model painting to a whole new level. However, before drybrushing, it's important to get to grips with shading using washes or inks.