WD-40 stands for Water Displacement, 40th formula. That's the name straight out of the lab book used by the chemist who developed the product. It protects the outer skin of the Atlas Missile from rust and corrosion. WD-40 spray is a multi-use maintenance spray. It protects metal from rust and corrosion, penetrates stuck parts like nuts and bolts and loosens them, displaces moisture and lubricates almost anything.