Petro is a prefix that comes from the Greek word “petra,” which means rock or stone. When added to other words, it often refers to something related to petroleum or fossil fuels derived from rocks and stones. For example, in the term “petrol” (or gasoline), the "petro" part of the word indicates that it is a product derived from crude oil - which itself comes from ancient organic matter buried deep underground, transformed over millions of years into fossil fuels through heat and pressure.