HSS stands for high-speed steel. This is the material typically used to make general-purpose drill bits, also called twist drills. Carbon steel bits are also available, and they cost less, but they're really only for drilling wood.HSS drill bits are sometimes coated in titanium nitride to improve performance. These are better for drilling metal. Beware, though: some manufacturers produce gold-colored drill bits because they look special. They might be coated, but it might just be color. Check before you buy.