What is "naphthene"

Naphthene \Naph"thene\, n. (Chem.) A peculiar hydrocarbon fraction occuring as an ingredient of some crude petroleums, mostly mixtures of derivatives of the five- and six-membered saturated cyclic alkanes, cyclopentane and cyclohexane, having the general formula CnH2n.

n. (context organic chemistry English) Any cycloalkane (or alkyl derivative).