According to the New York Times article on the death of John S. Barry, the man not responsible for the invention of WD-40 but the ubiquitous sale of the product, the name WD-40 stands for “water displacement, formulation successful in 40th attempt”.

Back in 1953 at the Rocket Chemical Company, it took employees 40 attempts before they figured out the perfect solution for a rust-prevention spray. Cool. I didn’t know that despite using WD-40 for just about all of my life.