The “brushless” part refers to the motor technology. Traditional electric drills use brushed motors — small carbon brushes contacting a commutator to switch the electric current and make the rotor spin. That contact causes friction, heat, wear, sparks, and friction losses.
A brushless motor replaces that mechanical contact with an electronic controller + sensors + permanent-magnet rotor. The controller electronically switches the current in the windings to rotate the motor.