Wiktionary
petroleum ether
n. A volatile petroleum fraction, usually available in a number of fractions boiling between 40°C and 140°C. Used as a solvent in the laboratory and industry.
Wikipedia
Petroleum ether
Petroleum ether is the petroleum fraction consisting of C₅ and C₆ hydrocarbons and boiling in the range 35‒60 ℃; commonly used as a laboratory solvent. The term ether is used only figuratively, signifying extreme lightness and volatility.