technically WD40 is a penetrating oil.....
I wouldn't even classify it as a penetrating oil since it has so little oil in it, <25%. The main ingredients, outside the petroleum oil, are an aliphatic hydrocarbon at 45-50% and LVP aliphatic hydrocarbon at 12-18%. Aliphatic hydrocarbons are like methane, ethene, ethane, butane, propane, etc.
Given that WD-40 is an absolutely horrible lubricant, and wasn't designed to be one, it's only really good for quick use on something that you go back and use a proper lubricant on later. See all sorts of people using WD-40 as a lubricant on moving parts, like on bicycle chains, with very poor results.