WD-40 is a brand of penetrating oil that is manufactured by the WD-40 Company based in San Diego, California. The name WD-40 stands for Water Displacement, 40th formula, and it was invented in 1953 by the Rocket Chemical Company. Its formula is a trade secret, and the original copy of the formula was moved to a secure bank vault in San Diego in 2018.

WD-40 is a water displacement spray containing a mixed blend of lubricants and anti-corrosion properties. Its job is to displace water, though it doubles up as a solvent and degreaser in one. It is used in households, trades, industries, and so much more. There are over 2000 official uses for WD40, and it is a household name, used in numerous consumer and industrial markets such as automotive, manufacturing, sporting goods, aviation, hardware and home improvement, construction, and farming.

In addition to the original WD-40 formula, the WD-40 Company also produces a range of other lubricants, degreasers, and rust removal products under the WD-40 brand. The company has grown to nearly 600 employees worldwide, and its products are marketed and sold in more than 176 countries and territories around the world.