Drillium is an old technique of taking a drill to parts to sculpt out some of the material to make them "lighter". In truth, the weight savings is probably negligible, but you get serious cool points for high grade drillium. Particularly if you didn't have any major component failure. I seem to recall seeing a pic of Eddy racing on some seriously drilled drops and being totally freaked out at the thought because those things had to be flexy and weak as all get out.