BRUSHLESS refers to the motor, which operates without carbon brushes which were historically (and still are) used in most power tool motors. The biggest benefit of operating without brushes is that the tool is more efficient, so it can operate for longer on a charge. For the DCN690 Cordless Nailer- it means that you can fire over 600 nails on a fully charged battery pack, and even the most trigger happy users should get through a day with two packs.